It's Cheaper to Throw Them Out
December 9, 2006 10:02 PM   Subscribe

Are reusable spacecraft history? Tonight's space shuttle launch was spectacular. Watch them while you can; there are only fifteen launches left before NASA retires the shuttle, and with it the concept of reusable spacecraft. Turns out that, despite previous efforts, governments just can't make the original, common-sense idea of reusable spacecraft economically feasible. Leave it to private industry to figure out how.
posted by Chinese Jet Pilot (37 comments total) 2 users marked this as a favorite
 
Common sense can often let people down. I mean to say something is a common sense idea is to say that it seems like a good idea before any real annalysis or evidence.

Also from your "economically feasible" link:

Engineers, of course, are not accountants. The very fundamentals cause confusion. Cost itself is very different from price. And the way cost is calculated can vary vastly according to which system of accounting rules and tricks are applied - a field which to engineers seems so much incomprehensible voodoo mumbo-jumbo.

What an absurd statement. If someone can handle differential equations for aerospace, they ought to be able to handle some basic accounting. In my view, something isn't "well designed" unless the entire life cycle is well designed.
posted by delmoi at 10:19 PM on December 9, 2006


Are reusable spacecraft history?

No, I don't think so. The link you posted states
In making this recommendation, this requirements change request cites the fact that somewhere between 20,000 and 25,000 pounds of weight could be saved in the design of the first stage by removing the systems needed to allow it to be recovered after it has been used.
So, if they make the change, they are doing it for the right reasons. However, the important bits that have to come back with the astronauts *will* be resusable. And that makes the most sense. It's not about the glory of having intact-looking spacecraft landing on earth after missions, it's about having a dependable, affordable space transportation system.
posted by Doohickie at 10:21 PM on December 9, 2006


And what delmoi said
posted by Doohickie at 10:22 PM on December 9, 2006


Crap. Nighttime shuttle launches are a big deal here on the First Coast. We head down to the beach and look south to see the plume of fire rise up out of (what appears to be) the ocean and arcs skyward. Nothing quite lights up the night sky like that gorgeous ship.

Of course, my wife and I are caught up in life and missed it.
*bangs head on desk repeatedly*
posted by Dantien at 11:24 PM on December 9, 2006


The real reason NASA pushed the Shuttle seems obvious. They didn't want to have what happened with the Saturn V program happen again. It's much easier for Congress to stop paying for new rockets than to stop refueling a fleet of already built multi-billion dollar machines.

NASA was convinced economies of scale were going to keep the [relative] costs down. And that, honestly, is what's failed. When they tried to get a once-a-month tempo going they lost the Challenger. When they invented an orbiting financial umbilical chord justifying the shuttle program, the ISS, we lost Columbia at a tempo of about every other month.

And I say this with love. I'm a space cadet at heart.


Dantien: Some of my clearest childhood memories are going out to Ponte Vedra Beach with my father to watch night launches.... and waiting, waiting for that rumble. When I got to college I used to pack my little Corolla full of friends and we'd make a run down to Titusville to watch them up close. There's nothing quite like seeing half a billion dollars burn up in eight minutes.
posted by trinarian at 11:51 PM on December 9, 2006


Want to save even more money? Get rid of the astronauts!
posted by b1tr0t at 11:57 PM on December 9, 2006


damn. this image is so cool. i wish we could be in a very douglas adamsesque future where that image was as commonplace as an airplane taking off of from a runway...
posted by weary at 12:09 AM on December 10, 2006


As tempting as it is to picture a blood-spattered Canadarm flinging goat carcasses into the void,

Worth the FPP just for that.
posted by dhartung at 12:18 AM on December 10, 2006


15 launches? In Shuttle terms I would expect that to be 2029-2031 or thereabouts.
posted by sourwookie at 1:34 AM on December 10, 2006


weary, I see your night launch and raise you a sunset launch.

[I was on the other side of the Indian River for this one]
posted by trinarian at 3:15 AM on December 10, 2006


So a question for anyone who might know –– is the aircraft-assisted shuttle-launch depicted in 'Superman Returns' actually viable?

I mean, that *is* an awul lot of fuel to burn, to get a payload off of the ground.
posted by vhsiv at 4:29 AM on December 10, 2006


awul = awful
posted by vhsiv at 4:30 AM on December 10, 2006


Want to save even more money? Get rid of the astronauts!

The best method is to pretend you have sent astronauts into space. The public pays more attention (and money) to the Buck Rogers shtick. Plus: choose the team like you'd choose a team of erotic dancers, then rework the uniforms. And if a supposedly piloted flight blows up, go into mourning mode and raise interest even more.
posted by pracowity at 6:20 AM on December 10, 2006


It's Kennedy's fault.

The US was on course to build vehicles similar to the shuttle in the early sixties, such as the X-20. Had effort been put into that, the shuttle would have been an evolutionary development, rather than a break from the trend.

However, Kennedy decided we needed to go to the moon. Spaceplanes, along with space stations and other things that would have created a sustainable space capability, were pushed to the side in a quest to go to the moon.

So, we landed on the moon a half-dozen times, and brought back some rocks. Was it worth it?
posted by MrGuilt at 6:24 AM on December 10, 2006


Well, I'd just like to relink Eriko's post on why the shuttle is as it is.

The shuttle's afforded many awesome shots, and inspired countless people by showing what humans (despite themselves, even) can do. I really do want to make it to one of the launches.
posted by Busithoth at 6:34 AM on December 10, 2006 [1 favorite]


weary writes: damn. this image is so cool. i wish we could be in a very douglas adamsesque future where that image was as commonplace as an airplane taking off of from a runway...

I don't know. I'd rather have The Thumb and a busy route nearby. The idea of a Hydrogen-LOX firebomb-deathtrap of a rocket seems really antiquated and uncivilized in comparison.

vhsiv writes: So a question for anyone who might know –– is the aircraft-assisted shuttle-launch depicted in 'Superman Returns' actually viable?

I do not know this "Superman Returns" nor its shuttle-launch, but launching from other aircraft has been done - both with Burt Rutan's SpaceShipOne and with the USAF's X-plane, among others.

It gets even cheaper if you launch from high altitude balloons, which has also been - at the least - tested and proven in concept. Free lift! Well, nearly. TANSTAAFL. Really cheap compared to lofting megatons in the form of an extremely complicated cryogenic fuel-oxidizer bomb.

I do not believe that oribital insertions have been made in either case, but it's merely a matter of proper aiming and fuel budgeting. And while either case requires additional engineering hurdles to overcome, there should be significant net gains in fuel and payload allowances to work with to overcome those hurdles, not to mention the advances in modern materials and technologies.


The SST is neat, but too complicated and expensive. This isn't entirely NASA's fault - the USAF had a lot to do with demanding certain features and capabilities, from payload capacities to downrange glide capabilities.
posted by loquacious at 6:38 AM on December 10, 2006


We can say all we want about how NASA screwed up the shuttle, and there are volumes of information about that. But the biggest problem is that with the shuttle - we bit off a lot more than we could chew (read: were willing to FUND to chew). The initial premise of the reusable space plane was a great concept, and the original DynaSOAR program that evolved into the STS program was more simple and more focused goals.

However, going into the early and mid 1970s, it became apparent that funding for NASA was going to dry up after the moon landings and that the development costs were spiraling. On paper the program looked good, but the engineers needed increasing amounts of time and money to work out the thorny physics problems.

Move into 1971 and 1972 and with Vietnam, a stagnant economy and oil spikes galore, money was vanishing from NASA's pockets and inflation was eating at the rest. So, NASA needed some help and the Air Force was more than willing to assist because they saw some great military benefits to the space plane.

Once the Air Force got involved, all sorts of parameters changed: they demanded a delta winged orbiter with a significantly larger payload area so they could capture US and Soviet satellites. They wanted the orbiter to reach polar orbits and be able to land on most any conventional runway.

These may seem like relatively small problems, but it increased weight, which increased the size of the motors required to place the vehicle into orbit. The landing requirements changed the aerodynamics and flight profile of the vehicle, leading to an almost wholesale re-design over what had originally been envisioned in the late 1960s.

In essense, NASA had far too many cooks in the kitchen which led to a vastly more complicated vehicle than they ever wanted. But in order to get the money to complete the project, they made these deals. And ultimately, placing politics before engineering, the current shuttle fleet and all of its flaws is what we have left.

Looking to the future, there are now great concerns about the development of the new Ares I and Ares V rockets to be used post-shuttle. There are many people criticizing the project stating that it is silly for NASA to spend billions to develop two new boosters when they already have a very welll tested fleet of commercial boosters that could (relatively) easily be man-rated (in the Delta and Atlas series of rockets). There are many others criticizing the two-launch approach being used to launch crew and cargo on separate vehicles.

I look more highly upon the space station and future moon projects than I do the current and future launch vehicles in NASA's fleet. The other projects provide us good test beds and challenges for our engineers to push the envelopes. As for launch vehicles - I'd almost rather see NASA leave that to someone else.

In fact, I'd like to see NASA evolve into a Lewis and Clark organization, whereby they blaze the trail and then turn over the technology and such to others to follow in their footsteps.
posted by tgrundke at 6:44 AM on December 10, 2006


The fundamental problem with reusable is simple: You *vastly* increase the mass of the craft.

Rockets are ruled by this equation:

Δv = ve ln(M0/M1)

M0 is the initial mass of the craft, M1 is the mass remaining after the burn generating the ΔV, and ve is the exhaust velocity, with respect to the rocket.

So, if you need to reach a specific delta-v, and you know the exhaust velocity, this tells you how large your rocket needs to be (M0) to put a given mass into orbit (M1.)

Why don't we have SSTO? This equation.
Why does the Shuttle's perfomance suck? This equation. In particular, that last term -- the mass in orbit. The Shuttle itself counts.

The Saturn V and the Shuttle can both put a great deal of mass into low earth orbit. The Shuttle, however, is stuck there, because it has to bring back around 100,000kg when it lands -- that being the mass of the shuttle, the life support wastes, and the crew. That's 110 tons of mass. You really see the difference in performance because of the dead mass. The Saturn V/Apollo put 33 tons into low lunar orbit. The Shuttle can barely get 4 tons into a geosynchronus transfer orbit. The difference? M0. All that came back from the Saturn V/Apollo was the six tons of the CM. The shuttle brings almost twenty times that much mass back.

Indeed, the Shuttle performs better, in terms of total mass, than the Saturn V in LEO. The shuttle can haul over 140 tons to LEO -- 110 + tons worth of orbiter and crew, plus almost 27 tons of payload. But since it brings most of that 100 tons back, increasing delta-v is incredibly costly -- M1 stays high, ve doesn't change, and you can only put so much fuel into the tank, so increasing ΔV is costly.

Thus, the core problem. The Shuttle tries to be a mass lofter *and* a crew vehicle. The fact that it does both is a testament to the engineers. The fact that it doesn't do either that well is a testament to the rocket equation.

A crew shuttle, with maybe 5 tons cargo to LEO, would be a vastly more workable solution for manned flight. The question is would it be cost effective? If we're not doing lots of manned shots, the answer will be no.

The reason for staging? This equation, which turns a boost-to-orbit from one equation to a series of them. The S-1C stage of the Saturn V didn't have to reach orbit, it just got the rest of the craft moving and higher, then got out of the way. This meant the S-II stack didn't need as much ΔV, since it was already moving at a good clip, and had a much lower M0, since we threw away the mass of the first stage.

So, the mighty first stage gets the rest moving fast, then goes away. The second stage gets the rest into orbit. The third stage gets the craft to the moon (we'll hand wave the lander here.) The fourth stage get the CM back to earth and lands it (Fourth stage? The Service Module.) Each one can do the job, because M1 keeps decreasing, which lets M0 decrease, and no single stage has to account for the entire ΔV budget.
posted by eriko at 7:41 AM on December 10, 2006 [6 favorites]


this thread rocks. thanks loquacious, tgrundke and eriko for the insight...
i know little of this specifics behind this matter, but i do want an interstellar future and however we most easily get there is best. (of course, i'll be dead by the time it happens but whatever)
posted by weary at 8:41 AM on December 10, 2006


The Roton is long dead - company went bust
posted by A189Nut at 8:55 AM on December 10, 2006


tgrundke, half of what you wrote was a nearly verbatim copy from dhartung 's [excellent] link. All the cool kids source, ya know. It's the new black.
posted by trinarian at 9:00 AM on December 10, 2006


Leave it to private industry to figure out how.

Build a non-orbital craft and then hype the hell out of it, pretending that it's an actual real spaceplane?
posted by Artw at 10:00 AM on December 10, 2006


trinarian, eriko linked to the piece by Maciej also. (It's over a year old, and has been linked here before.)

What's really encouraging is that NASA Administrator Griffin is saying similar things. They're in line with current policy, though, so many it's not all that revolutionary.
posted by dhartung at 10:07 AM on December 10, 2006


All this tech talk. The fact of the matter is this. Before the internal combustion engine, people discussed ways to make the horse run better. Essentially, and I mean at its core, this is the same scenario with better "legs." [clears throat]

Space elevator? Inspired nonsense.

Changes will take place - changes which are outside of our contemporary imaginative abilities - and then we will live off-planet in space. And more than likely (guaging changes and breakthroughs that happened in similar period of times at the head of previous centuries), this will happen within nine years time, before 2015.

You see, all the small talk about space and living off-planet is just that, small talk. To make it happen, some basic but critical discoveries and developments must take place. Until then, all this talk about space is like a person from the 19th Century postulating on 20th Century video gaming ie unlikely, unfeasible, and unrealistic.

If you are interested in space - and from my perspective, most kids have their heads far better around this than many adults - let go of pre-conceptions, get out of the box, and expand your (event) horizons.
posted by mongonikol at 10:37 AM on December 10, 2006


BTW, this quote deep from within from the post about Nikola Tesla seems particularly pertinent...

"Tesla, who died in 1943, "unleashed a revolution," declared Wagner. "People were riding on horseback in 1896, and 73 years earlier, in 1823, people were riding on horseback. But advance 73 years -- after Tesla's polyphase system was used at Niagara Falls and took electric power to Buffalo and New York City -- to 1969, and that was the year man walked on the moon. You try to tell me it wasn't polyphase AC and the wide dissemination of knowledge through radio that made that possible. It had to be that."

One of us is going to develop/reveal/discover a Reallygreatwhopping Thingamadoo, that is going to turn the world upside down on its hat (levitation? limitless power?), at which all of us, en masse, will cease doting about in the present, dawdling over past achievements, and begin looking forward again, to a bright, inspiring, and exciting future.
posted by mongonikol at 10:51 AM on December 10, 2006


they demanded a delta winged orbiter with a significantly larger payload area so they could capture US and Soviet satellites.

Huh? How is the shuttle, which only goes to an altitude of a few hundred miles, going to "capture" a Soviet satellite, most of which orbit at several thousands miles? And how is it going to stow it onboard to bring it back without custom made cradles built to withstand landing loads? That statement makes no sense at all.

There are only a few examples of recovery of satellites that were not intended to be recovered, such as the Palaba B2 and Westar recoveries done in the 1980s. The only reason they were available for recovery is that they were stuck in the shuttle Low Earth Orbit due to the failure of the the solid rocket motors intended to send them to a usable geosyncrhonous 22,300 mile orbit.

You just don't go plucking satellites out of space.
posted by Doohickie at 3:28 PM on December 10, 2006


How is the shuttle, which only goes to an altitude of a few hundred miles, going to "capture" a Soviet satellite, most of which orbit at several thousands miles?

Simple -- they didn't. Spy sats are, as a class, in low polar orbits. It's a matter of optics -- it's easier to see something from LEO at 75-150 miles above the ground than it is from geostationary orbit 22,000 miles above the surface.

Certain area scan recon sats would be in geostationary orbit (or even higher, if they needed to be out of the Van Allen belts.) but the photo recon sats were, and still are, launched into very low polar orbits.
posted by eriko at 3:41 PM on December 10, 2006


Doohickie said: How is the shuttle, which only goes to an altitude of a few hundred miles, going to "capture" a Soviet satellite, most of which orbit at several thousands miles?
...
You just don't go plucking satellites out of space.


eriko said: Simple -- they didn't. Spy sats are, as a class, in low polar orbits.

As long as a target satellite (or its parts) fit completely into a Shuttle's cargo bay, capture and return to Earth is entirely possible. To review:
  • November 1984 — without any great difficulty, STS-51-A retrieved the Westar 6 and Palapa B2 satellites (photos) and returned them to Earth.
  • May 1992 — STS-49 rendezvoused with the INTELSAT-VI 603 communications satellite some 200 miles up, placed it on a stand in the open cargo bay, and attached a rocket motor that later moved the satellite into its planned geosynchronous orbit at 22,300 miles.
  • December 1993, February 1997, December 1999, and March 2002 — Shuttle crews admirably demonstrated their repair capabilities during the Hubble servicing missions.
Shuttles have flown several classified military missions, but have there been any credible rumors of a space-based version of Project JenniferWP?

Perhaps I've just seen You Only Live Twice too many times...
posted by cenoxo at 8:50 PM on December 10, 2006


Regarding SSTO (Single Stage To Orbit) vehicles, it's a neat solution but the downside is that this type of vehicle is mostly fuel with a small payload area so isn't awfully practical as a cargo-carrier. Perhaps sometime in the future they might use this type of vehicle as a personnel shuttle, here's hoping.
And Roton was very, very cool. It's a shame that it went bankrupt, it would have been really neat watching the return of a 'helicopter from space'.

Regarding this new class of launch vehicle, I feel it is a step backward. And manned missions to the moon is a big step in the wrong direction considering this country's economic situation right now and the amount of funding it will pull away from other unmanned programs.
I have been a big fan of manned spaceflight since the mid to late 1960's (watched the first manned moon landing on live TV as a child) and could talk all day about manned and unmanned spaceflight both U.S. and Russian programs but this business of going back to the moon now with this country's finances in the shape they are now, with basically recycled Apollo equipment is a crock.
There should be a shuttle replacement for sure, but not the type of spacecraft they're planning for now, or the manned programs to the moon (and possibly Mars) they are planning for now. Perhaps five to ten years from now when the economy is in better shape, but at this time there should be more focus on unmanned spacecraft, including orbiters, landers and rovers than the solution they are pushing for now.
posted by mk1gti at 10:00 AM on December 11, 2006


"Thus, the core problem. The Shuttle tries to be a mass lofter *and* a crew vehicle. The fact that it does both is a testament to the engineers. The fact that it doesn't do either that well is a testament to the rocket equation."

Seems like it would make sense to divorce crew launch from cargo launch then. Since we've already got working crewless systems for delivering cargo to the ISS (Russian Soyuz-type ships), it seems reasonable to think we could do the same with heavier cargo lifts, or just more lifts of lighter vehicles.

"A crew shuttle, with maybe 5 tons cargo to LEO, would be a vastly more workable solution for manned flight. The question is would it be cost effective? If we're not doing lots of manned shots, the answer will be no."

However, we've already got quite a few booster designs that can loft 5 tons to LEO easily, so at least we really don't need to do any more heavy R&D on it. 5 tons to LEO is Gemini Program level; between us and the Russians we've probably got several hundred suitable boosters moldering away in underground silos in Montana and Siberia.

I'd posit that being able to put a crew to the ISS for $100 million rather than $1.5 billion might actually stimulate more launches, but that probably also depends on what we've got to heavy-lift. Is there anything else besides Energiya that can put 30 tons in LEO?

I wonder if a version of the Shuttle launch system minus everything but the Main Engine section of the Shuttle could be worked up? Mount a non-reenterable cargo sled - just a big cylinder with a fairing maybe - where the Shuttle normally goes now, with the SSME's right behind it where they normally sit, maybe with an aeroshell (balloon-based?) and recovery system for the engines, or maybe not.

Hmm. Maybe I'll do some sketches of that...
posted by zoogleplex at 2:39 PM on December 11, 2006


like this?

Ares V
posted by b1tr0t at 3:04 PM on December 11, 2006


Hey, that's pretty neat b1tr0t, but actually I just meant subtracting all parts of the Shuttle Orbiter except the Main Engine section and replacing the removed mass with a cargo sled type thing.

This here, that would be what I'm talking about.
NASA has recently resurrected the idea of the Shuttle-C concept in the form of the Shuttle Derived Launch Vehicle, currently known as SDLV. As of June 2005 the proposal is reportedly finalizing into the form of a 120 metric tonne payload with an in-line design, now known (July 2006) as Ares V. If chosen, this will be significantly different to the original Shuttle-C reference layout.
The Ares V looks pretty interesting, and seems to be what they're actually developing. I like that for the V they decided to go back to the RS-68 engine, which is cheaper and higher thrust than the SSME.
"While NASA calls the central booster tank "a larger version" of the Space Shuttle External Tank, it should be noted that its 10 meter (33 foot) diameter matches that of Saturn V's first (S-IC) and second (S-II) stages, and is roughly the same length as the two stages combined."
Which goes to the Rocket Equation; you have to have the same mass of fuel to make the heavy lift. Of course it's going to be like a Saturn V. That monster turned out to be well-proven tech with a perfect flight record. How about that von Braun guy, huh?

This looks like the right direction - well-established, proven tech re-assembled for effective re-use. Looks like NASA's on the right track with this.

OK, so much for the heavy lifter, 130 tonnes is great.

So, the Ares 1 is the new crew lifter? I guess the SRBs are proven safe and effective as long as you launch at over 40 degrees F ambient temp... and in this case, even if the O-rings fail there wouldn't be a jet of hot gas torching a big fuel tank, as the payload is all on top of the booster instead of on the side. While at first that seemed startling, on paper it looks like a good idea. SRBs are super-cheap. However, they burn pretty rough - there's going to have to be a really good stability solution in place to keep the firecracker on course...

Still, sounds like NASA's got their ducks in a row on this one. Relatively low R&D overhead, proven tech, relatively inexpensive components. I like it, makes me feel better about what they're doing.

However, I still think we should learn how to build a long-term, sustainable, safe and reliable human habitat in space before we start trekkin' out to Mars...
posted by zoogleplex at 4:18 PM on December 11, 2006


I guess the SRBs are proven safe and effective as long as you launch at over 40 degrees F ambient temp

What killed Challenger wasn't the fire from the SRB, or even the explosion. What killed her was aerodynamic forces ripping her apart when the plume of fire from the leaking O ring caused the strut holding the SRB onto the tank. It pivoted out, so you had 14MN of thrust pushing along the path of flight, and 14MN of thrust pushing along a different vector. The shuttle twisted in the air under the differential thrust, while traveling at Mach 7, and drag destroyed the craft in less than a second -- so fast that both SRBs kept flying until destroyed by the RSO.

The idea of the stick is 1 SRB is far safer than two. If it doesn't light at launch, you, well, get off the spacecraft and try again later. With the Shuttle, if one SRB doesn't light at liftoff, the Shuttle dies, the pad dies, and probably a bunch of people in the crowd die -- it all depends on where the ultimate land shark ends up.

Plus, with the 2nd stage on top, not next to, the first, you don't have the lateral force concerns that plagued the shuttle (and doomed the Shuttle-C variant.) You can even theoretically survive a CATO of the first stage if you have a couple of seconds of warning, since you can put a rocket on top to pull the crew capsule away. A leaky O ring just makes a scorch mark.

5 tons to LEO is Gemini Program level; between us and the Russians we've probably got several hundred suitable boosters moldering away in underground silos in Montana and Siberia.

Not quite. ICBMs move 1-2 tons suborbital, though bolting on new top stages works (see, Thor-Able, Atlas-Agena, etc.)

You need more than 5 tons to LEO -- I said "crew + 5 tons cargo", which is more on the order of 20 tons, depending on how many crew and how long.

I wonder if a version of the Shuttle launch system minus everything but the Main Engine section of the Shuttle could be worked up?

Shuttle C -- replace the orbiter with a cargo pod with the SSMEs mounted on them. Workable, but you still have the side-slung mass problem.

The Ares V, which was the SDLV (Shuttle Derived Launch Vehicle) was originally going to be a new first stage with 5xSSMEs and 2 or 4 SRB, with a new 2nd stage (also with SSMEs, modified for air start and restart.) Then they really thought about the problem.

1) The SRBs assume that you'll have long burning engines firing in tandem with them. As solo boosters, they really need to be longer, and longer would be handy for higher orbits or GTO/LTO insertion.

2) The SSMEs are amazing engines, but if we're not going to reuse them, there's lots of extra features on them that we aren't using. Extra features are mass. Mass you aren't using is bad in rocketry.

3) For that matter, SSMEs are built to ground start, once, then fly until fuel exhaustion. The 2nd stage SSMEs will need to be modified for air-start and restart. That won't be cheap.

Back to the drawing board. Longer SRBs are easy -- longer tube, more fuel. The Shuttle SRBs have four segments, extending to five is pretty trivial -- just bolt another segment on. It'll take some extra structure, but it's not a huge problem.

The engines are harder. The first stage is the easier answer -- pick the engine built as an SSME that isn't going to be used more than once, the RS-68. Bonus, proven engine, and 50% more powerful, and cheaper. Not reusable, not man-rated -- neither is an issue on a heavy single flight cargo booster.

So, now, 2x5 segment SRB Stage 0 and 5xRS-68 stage 1, total liftoff thrust around 43MN, with longer burn times on both Stage 0 and Stage 1 -- the first stage is about the same diameter as the S-1C of the Saturn V,, and as long as the S-1C and S-II together. Yeah, that's a good start -- heck, if NASA had that in 1967, we'd have landed four guys on the moon.

But what about the second stage?

So, they think about it, and Rocketdyne goes "You know, we did a bunch of work on the J-2S. We could easily restart the line, and swap out parts with new alloys, get 1.5MN easy, maybe 2MN)

NASA stops. 1.5MN? Air start? Restart?

Well, yeah, the J-2 was made to do both. We got 1.1MN out of the J-2S in 1970. Heck, just swapping the pump with something made this decade would get 1.5MN.

Sold. This is a little less thrust than they'd banked on, the SSME being able to run 2.1MN, but they can trade that off with a longer burn, and making an existing air start/restart engine more powerful is much easier than making a ground-start only engine into an air-start, much less a restart.

Of course, we're now talking new stage bodies, longer SRBS, Delta IV and Saturn V engines, vertical stack -- the SDLV isn't looking so Shuttle Derived anymore.

But it does look like a workable booster. We know all the parts work in at least basic form -- the RS-68 is done, the 5 segment SRB is a fairly trivial change. The J2X will take more time to build up, but no more than the SSME conversion would, and the J2 is proven on the moon mission.

Meanwhile, you take one of these SRBs, you put a version of the 2nd stage onto it, and you have your crew lift vehicle. This means that both craft are using common parts.

And now, we're almost *pre* Apollo. This setup is known as Earth Orbit Rendezvous. Send a spacecraft up on one booster, send the crew up on another, have them meet, board, and go to the moon. It was EOR or the Direct Mission that was fighting it out in the halls of NASA, but EOR looked too complicated, and Direct required the Nova booster, which was getting bigger (thus, harder to build) by the day.

The winner? Neither. We went with Lunar Orbit Rendezvous. Send a big (but not nearly as big) rocket to Lunar orbit. There, a lander separates and lands, with part of the crew. They then leave half the lander behind, meet up in Lunar Orbit, abandon the rest of the lunar lander, and fly home.

It worked. But we've beaten the rendezvous problem, so if an Ares V can't get the craft into orbit, we'll send it in two pieces. Thus, EOR is the new black.
posted by eriko at 9:04 PM on December 11, 2006 [1 favorite]


Well, sweet! I think this course is a good one then. There's not a hell of a lot of payload that right now exceeds 143 tons, so I think the Ares V will do well. Add the ability to do automated rendezvous, and we could theoretically build some pretty big structures up there with little human intervention.

I really don't think we should send people on a 3-month or 6-month flight to Mars in a tiny little Orion capsule... I think we should try to aim for something larger that we can spin for gravity, or maybe at least something we can spin using a tether with a counterweight, so our crew doesn't experience the physical degradation of microgravity. Besides, being cramped with 5 other people in a volume the size of a smallish house trailer would be pretty torturous. And we're not even mentioning the dangers of solar and cosmic radiation. I put some of my thoughts about it in the moonbase thread, here's an excerpt:
Man. Why does everyone want to live on "land" in space?

How about we try to get good at just plain living in space first? As in, how about we learn how to build relatively large space habitats like all the L-5 or O'Neill Colony type things, big torii or cylinders that we spin for enough gravity to keep us healthy, and which can carry enough mass in their shells to shield us from radiation? Even a cylinder 30 meters across and 100 meters long could hold a fairly large number of people and possibly enough biomass and machinery to create a long-sustaining (if not self-sustaining) biosphere.

Once you can get something like that - a large, relatively safe place for a number of people to inhabit in space - working well, you can strap some thrusters on it and send it anywhere you want to. If that works, it doesn't matter that it might take a couple of years to get to Mars, or for that matter anywhere else in the system, because we've got a long-lasting "home base" to stay in for the trip.

...

Build that, then spin it a little, maybe 1/10 g, maybe even 1/6 g to equal the moon's gravity, dump in half a meter of sand around the entire "floor" for some rad shielding, and then, well, put in all the housing infrastructure and then spin it up to 1/4 g or even 1/2 g. How hard is it for us to build a 60-foot by 240-foot hollow aluminum tube? We build 50-foot by 500-foot submarines, fer cryin out loud, and they take exponentially more structural stress! Hell, we could start with one that's 60 feet by 20 feet, and tack on more just like it to extend it out over time.

We should figure out how to put a crew of 40 or so in one of those and live there for 5 years before we try going out to Mars, I think.
"The shuttle twisted in the air under the differential thrust, while traveling at Mach 7, and drag destroyed the craft in less than a second -- so fast that both SRBs kept flying until destroyed by the RSO."

*shudders* yikes. I didn't realize it wasn't the explosion.

And I'm sure glad we've never had an SRB fail to light... that would be truly ugly.
posted by zoogleplex at 2:05 PM on December 12, 2006


I think we should try to aim for something larger that we can spin for gravity, or maybe at least something we can spin using a tether with a counterweight, so our crew doesn't experience the physical degradation of microgravity.

Sounds like the Mars Habitat Unit proposed as part of Mars Direct.

We should continue to send robots until the Mars Curse is overcome.
posted by b1tr0t at 2:45 PM on December 12, 2006


Yes, the MHU is exactly what I was talking about, I've seen that and it looks pretty interesting. However, I would consider that an absolute minimum living facility for such a long trip, and I think we could do something more ambitious. We're talking about more than a year in space here...

"We should continue to send robots until the Mars Curse is overcome."

Which is precisely why I'd like to see us do a much larger, long-term space habitat beforehand, to send a much larger crew to Mars, a "five year mission," even.

It might be possible to send that space hab to Mars as a permanent base, especially if the folks who land on Mars can (as hoped) set up their own rocket fuel manufacturing facilities, which could fuel their return to orbit and allow us to rotate smaller crews from earth to Mars and back.

That's a big jump though. We could probably send a few extra redundant backup ships out to Mars. I guess in theory, being able to lift 143 tons at a time we could build a pretty big ship, with lots of onboard fuel, in 4 or 5 launches. Better than sending people off in a tiny tin can!
posted by zoogleplex at 3:03 PM on December 12, 2006


I guess in theory, being able to lift 143 tons at a time we could build a pretty big ship, with lots of onboard fuel, in 4 or 5 launches. Better than sending people off in a tiny tin can!

We're talking about the same to LEO as the Saturn V did -- Skylab in one shot. One of the early Skylab proposals involved a "wet lab" -- the lab would be used as tankerage for the launch, then refitted as a habitat. Skylab's grid floors are a mark of that heritage, though Skylab was lofted dry.

Fuel is tough, esp. dense fuels like RP1 and the various hypergolic fuels, and one thing we're not very experienced with is transferring cryogenic fuels in large quantities. The obvious way to get fuel for an interplanetary craft into space is to pull the engines off the last booster stage and replace them with a fuel transfer adapter -- the tanks are already built to the correct proportions and can handle the fuel/oxidizer used by the stage normally. This does mean that you need to use the same fuel/oxidizer combo, which may not be workable -- storing LH2/LOX for a few hours before launch or a few days trip to the Moon is one thing, storing them for the months of transit to Mars is another.

All that aside, it is pretty clear that the ~150 tons to LEO isn't going to be enough to loft an Interplanetary Craft + supplies in one shot. I suspect that it may take three -- one for the lander/return stages, one for the outbound stage, and one for fuel. Assuming hypergolic fuels, ideally, you'd be able to loft the two parts of the craft with one part of the fuel on board, so that the tanker shot only has the other, which makes building the tank easier, and increases the safety margin. Bonus -- you only need to transfer one liquid.

Another factor -- the Ares V might actually be able to loft more. The current sketch is 2xSRB as stage 0, and 5xRS-68s as stage one. It wouldn't be impossible to add two more SRBs, which would increase the thrust by more than 40%. The big question then becomes could the first stage (which is transferring the thrust from the SRBs and itself to the 2nd stage) be able to handle the load? We're talking somewhere in the neighborhood of 60MN of total thrust between the four boosters and the first stage, nearly twice what the Saturn V had at launch. That's a great deal of load on the first stage. If it can handle it, 200+ tons to LEO in one shot is possible.

Another possibility is not going cryogenic with the first stage, and using RP1-LOX and the RD-170 engine. There's lots of very good reasons to not use LH2 as a fuel in the first stage, and they all have to do with the density issue.
posted by eriko at 12:39 PM on December 13, 2006


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