The Case for a Small CEV

John Creighton · 2005-08-13 23:51:02

http://www.marssociety.org/news/2005/0704.asp

Anyone read this? Zubrin strikes me as a man that is in a real rush. I don't see anyone outright lies and it is an interesting read. However, I think the philosophy is wrong. Having one or two orbital rendezvous will not make the mission too risky and it will substantially increase capabilities.

GCNRevenger · 2005-08-14 01:13:40

Rush? Now there is an understatement of biblical proportion...

Bob's direct moon flight plan is a pretty BAD idea if you wanted to actually DO anything on the Moon. Notice how the big HLLV rocket is only able to deliver the CEV capsule to the surface with just enough fuel to get home again, which means that you get basically zero payload on your Moon landing. The simplicity of direct return from the Moon comes at the cost of efficency... its fine if all you want to do is repeat Apollo, but not so good otherwise. I think that Bob also grossly overstates the problem of the additional risk for orbital redendezvous, which is pretty reliable now. The bennefit of not having to lug the Earth-return fuel off the Lunar surface, and the bennefit of having ~140MT total mass instead of <110MT (big SDV plus Stick instead of just SDV) is really important.

Since we want to go to different sites on the Moon for a variety of reasons (science at various sites, interferrometer telescopes, communications towers, prospecting promising craters, look for buried snow, etc) then it makes sense for whatever vehicle the crew lands in has to carry a little payload with it too. This is vital and non-negotiable. It is also great for Lunar bases, since the lander could bring all the food and supplies needed for their whole stay without needing an additional launch from Earth... Kind of like getting a free Progress with your Soyuz.

I am also VERY unhappy with Bob's talk of using CEV and SDV to lift ISS modules: using SDV to launch them would require us to go the Shuttle-C route, where a cramped cargo faring rides on the side of the old Shuttle stack equipped with attitude control systems. This is a terrible configuration since it can't be used to launch Mars vehicles later on... I find it odd that Bob skipped that part.

Any talk of less then four crew to the Moon is also right out.

Ad Astra · 2005-08-14 22:13:20

It looks like Zubrin has renounced the "Moon Direct" plan he advocated in "Case for Mars." He used to support two HLV launches (one for the fully-fueled return vehicle, one for the habitat lander,) with a rendezvous on the lunar surface. A similar idea was used by NASA's "First Lunar Outpost" study, which envisioned the Saturn-derived "Comet" booster.

A two-launch scenario like the one Zubrin originally wanted makes much more sense than what he's proposing now. That way you can land decent-sized payloads on the moon and let the humans stay for extended periods of time so they can perform real science. Weight growth becomes a fear of the past.

C M Edwards · 2005-08-15 13:50:21

I don't believe this rises to the level of heresy.

Most of Zubrin's statement is just discussing the requirements to send a crew return vehicle (remember the ERV?) directly to the moon if it will be using a direct return to get back. Applying those limits to the CEV won't necessarily hamper a moon mission if 70% of its hardware arrives on another rocket. There's no renunciation of "Moon Direct" here, and, IMHO, nobody's flying to Mars with nothing but a CEV, anyway.

The blurb about finishing the ISS is chilling (typed by Bob's own hand *shudder*), but this course has to be considered. The International Space Station will not be safely at the bottom of the Pacific by the time work begins on a heavy lift vehicle. NASA will probably try to wed any new HLV to the ISS just out of general principles. We shouldn't just sit back and enjoy the ceremony, but we must be prepared for this eventuality.

GCNRevenger · 2005-08-15 14:19:50

"won't necessarily hamper a moon mission if 70% of its hardware arrives on another rocket"

I disagree, in fact I disagree quite strongly: many Lunar missions will be landing at sites besides the "base camp" at many different locations to do a variety of tasks:
-Geology and other science
-Prospecting for minerals
-Telescope array deliver and setup
-Communications hardware setup
-Searching for Lunar water and He3
-Test mining and Mars equipment and techniques

To do these things, you will need to send several tonnes of payload, but not much more then that. For such light payload lifting, it makes much much more sense just to increase the capacity of the lander and launch vehicle and send the needed items (telescopes, heavy rovers, multi-meter drills, soil ovens, communications towers, etc) with the crew instead of paying for a seperate rocket, a seperate TLI stage, and a seperate lander.

You get the added bennefit of having the ability to deliver heavier payloads to the Moon if you want to move something big (a MarsDirect/NASA DRM sized HAB, heavy fuel plant, etc), plus if the crews only need a few tonnes of supplies (food, water, suit spares, etc) for their 6mo stay then you don't need to pay for as seperate supply mission.

To do it any other way doesn't make sense... In order to bring these extra tonnes of stuff along, a single direct shot to the Moon is just not practical even with the huge 110MT launcher. Send the crew up seperately in their own capsule, and send up a dedicated lander and TLI stage on the heavy lifter, dock in LEO, and then transfer crews and go down to the surface. This avoids needing to man-rate the big HLLV, which will never be as reliable or safe as "The Stick," and radically increases the available payload. It also opens the door to future reuseability, where Bob's plan does not.

Edit: Oh! And for early missions, missions to the Lunar poles, or extended duration missions the payload could be used to carry extra propellant or fuel cell/life support supplies.

C M Edwards · 2005-08-15 15:22:48

Ah! Bob's plan gives up the dream HLV. Got it. 8)

Grypd · 2005-08-15 17:15:54

Ah! Bob's plan gives up the dream HLV. Got it. 8)

It does a bit more than that it actually will put the crews sent to the Moon at more risk. Though I would prefer different the crews will arrive with nothing prepared before-hand so they will need to take every thing with them to make there habitats and to actually start there mission. If though they are sent in a lot smaller craft they have to make extremely sure that they land close to there supplies. If they make a navigational error on the way down and find themselves too far from the supplies this could prove a problem. (the sun playing up even when its supposed to be quiet etc etc). With the lack of an automated triangulation system and our very poor maps of the Moon (they are give or take a 100km in some places, the poles for instance) this could easily happen.

Im not sure why Bob dislikes the NASA plan to actually have a rendezvous before they send equipment maybe he just dislikes the whole idea of rendezvous in the first place. We already know his opinion of the Moon and maybe this is just an attempt to simply get the Moon part of the NASA plan to be treated as a joke and to concentrate on Mars. If that is the case though it is likely if this actually occurs then it will also put a hammer blow to NASA eventually going to Mars. With statements "but all we did was another blasted Apollo lots of pictures nothing else and so why go to Mars to do the same". Nope I would be circumspect about the reasons "Honest Bob" has put the statement out.

SpaceNut · 2005-08-15 19:37:09

If all that is needed is a quick crew rotation vehicle, then it would fit this bill. But definitly not for long duration,

GCNRevenger · 2005-08-15 21:25:32

A "quick rotation" is not what we need for initial missions, we need at least some payload with the crew to do anything but repeat Apollo, and the heavier the cargo-only version is the better.

Bob's plan also requires the big HLLV carry people, which is not a good idea from a safety standpoint (same deal with MarsDirect actually) and would cost alot of money to man-rate it.

Oh, and his lander/return stage burns Hydrogen so that it can juuust barely lift a vehicle big enough to hold maybe four people. Hydrogen boiloff would prevent any extended stays, since you would have to return home in short order before your fuel all floats away... Definatly not a real plan.

idiom · 2005-08-16 00:36:04

What we need on the moon is something huge that will break down if left unoccupied. Thus teaches the I.S.S.

Every way I look at it MD needs a bigger launcher. Each item in the linked article seemed to destroy our chances at MArs in order to smite the loonies.

SpaceNut · 2005-08-16 05:13:35

I am all for a HLLV for moon missions for cargo but I thought we had learned a lesson with the shuttle in that mixing the manned and cargo was a bad concept at least for launch.
Maybe just joining them once in orbit or on the way much like the LEM and Apollo did. But then again we want to go to the moon often and fast, so a mixed asortment of vehicles would be the prefered.

GCNRevenger · 2005-08-16 07:33:20

We're not talking a huge amount of payload here, but the crew lander ought to be big enough to carry a pressurized rover, a prefabricated telescope, a multi-meter drill, or all the supplies a crew would need for a six-month stay at the base. Extra fuel would make extended stays at remote sites too. Just a few tonnes.

A mixed assortment of vehicles is unessesarry, we are better off building only the "big" kind of vehicle rather then spending money developing the "small" kind. Since the big version could carry supplies as well as crew, you could save having to sending stuff like water, food, and space suit parts on seperate vehicles.

Commodore · 2005-08-16 13:59:45

Remember were talking about spiral 2 missions here. No longer than 14 days, or 1 lunar day. There isn't going to be time for building. Spiral 2 should be all about geology so we have a good idea of exactly what we have to work with.

A pair of solar powered 2 man rovers will all the gagets a geologist could dream of built in is all we need. And if we're smart we'll make them capable of teleoperation so the science can continue long after we go home.

C M Edwards · 2005-08-16 14:06:12

A mixed assortment of vehicles is unessesarry, we are better off building only the "big" kind of vehicle rather then spending money developing the "small" kind.

While I'm not going to agree with this unconditionally, I've got to admit that there's logic to it. Heavy lift launch vehicles are the most efficient for reaching orbit, and are arguably the best option for many applications. Diversity can wait until after we're out of the well.

Zubrin's little moon proposal needed a HLV, and a SDV is the HLV that NASA most desires. So, apparently, he decided to settle.

That's not heresy, and it's not an attempt to submarine manned moon missions. It's just...

... complacent capitulation! :?

All right, who is this guy, and what has he done with Robert Zubrin? :shock:

C M Edwards · 2005-08-16 14:11:27

Remember were talking about spiral 2 missions here. No longer than 14 days, or 1 lunar day. There isn't going to be time for building. Spiral 2 should be all about geology so we have a good idea of exactly what we have to work with.

I'm not sure that "spiral" should be used to describe an aeronautics program. :?

Rxke · 2005-08-16 15:07:48

we are better off building only the "big" kind of vehicle rather then spending money developing the "small" kind. Since the big version could carry supplies as well as crew, you could save having to sending stuff like water, food, and space suit parts on seperate vehicles.

And make it remote control-capable, so you can drive it to new landing places, maybe?

Ad Astra · 2005-08-16 17:04:08

I'm not accusing Zubrin of heresy here; I just think that he's giving up on the superior "Moon Direct" architecture for a mission that can be done cheaper and faster (but not better.)

I think Zubrin's primary motivation (made clear by his presentation at the Mars Society convention) is to quickly develop a moon program to the point where it has too much momentum to be killed by the incoming administration in 2009.

Zubrin is underestimating the political concensus that the Vision for Space Exploration currently enjoys. The challenge is to build an image of an "American Space Plan" instead of a "Bush Space Plan." For now, the forceful support of a few key lawmakers like Tom DeLay and Kay Bailey Hutchinson has gotten the VSE the funding it needs. Perhaps they will stick around long enough to sustain the plan after 2008. Maybe the public support can be built to the point that it will be political suicide to cancel the VSE.

When you give people the choice of VSE or the Shuttle-ISS, ten out of ten will decide in favor of VSE. When you start giving them large numbers about how much VSE might cost, they'll oppose VSE to the bitter end.

TwinBeam · 2005-08-16 22:01:22

Why not consider Zubrin's approach as a core capability, but plan to build around it when you want to do more than a single launch can handle? Nothing says you can't still do two launches if a mission calls for it, but why not have the option for single launch?

Two big launches shouldn't cost a lot more than one big and one small (crew) launch, once you count NASA's fixed costs and support costs for each launch, and given some savings by only developing one launch vehicle. You'd get more net payload to the moon than with a small crew launch and a big cargo launch.

The main issue I see is making sure not to compromise crew safety trying to maximize cargo capacity of the CEV. But the answer there is "just don't compromise". Shuttle had many bigger safety issues than sending cargo up with crew.

GCNRevenger · 2005-08-16 22:41:54

Zubrin's "core capability" CAN'T be built around without sacrificing the simplicity, safety, and just plain good sense of launching the crew on a dedicated vehicle and putting light payload on the crew lander.

What do you think the astronauts will be doing on the Moon? Whatever they will be doing, you can bet that they can't do it without a few tonnes of payload. Even if you are just sending a crew rotation to a base, they will need to have a few (and only a few!) tonnes of supplies. Its just stupid to send an additional flight with its own rocket, TLI stage, and lander - plus hoping that you actually land near the crew/base - rather then simply making the lander a little bigger. Zubrin's plan is terribly inefficent because it needs extra fuel compared to NASA's Lunar orbit rendezvous method, so even with the largest practical SDV and a lander burning Hydrogen fuel, it can just barely carry a capsule there and back - no extra payload is possible!

There is also a major safety issue, that putting the crew on the massive SDV launcher is no where near as safe as putting them on their own dedicated SRB-derived vehicle. NASA and Lockheed figures peg the difference around three times less safe. The cost of making the big SDV three times as safe to be on par with a rocket with a third of the engines is impossible to do for any reasonable cost, a safety compromise would have to be made. There is also the safety enhancement of not leaving Earth orbit until after the entire vehicle stack can be put through diagnostics to ensure that it withstood launch without damage.

"Two big launches shouldn't cost a lot more than one big and one small (crew) launch"

Magnum SDV:
$60M tank
$60M SRBs (two, aprox)
$225M SSMEs (five, $45M each)
~$15M upper stage
=$360M total

Stick for crew:
$35M modified SRB
$45M SSME (one)
~$15M upper stage
=$95M total

I disagree, I think it is clear that the SRB launcher will be radically cheaper then the big SDV HLLV, particularly when you include the much larger assembly costs. The SRB launcher will not be that hard to design, since the first stage can be used almost as-is and the upper stage engine is in production today.

With these things in mind, I think it is very clear that it would be a waste of time and money to develop a direct flight mode

TwinBeam · 2005-08-17 14:39:11

GCNRevenger:

COST:
You've listed vehicle costs - but what about the ground support for two different ships, development costs - typically a substantial multiple of the actual per-ship costs - and fixed budgetary costs? All of those tend to dilute per-launch cost differences, and some of them will be higher for two very different ships than for two highly similar ships.

More importantly, you tend to get what you pay for - even ignoring cost savings from using a larger rocket, you'd still get more payload to orbit in rough proportion to the higher vehicle costs. So Zubrin's approach doesn't have to mean less payload to the moon - just launch one rocket with a CEV and decent payload, and launch another rocket with a fuel tanker to extend the range of the first.

SAFETY:
A "one stick" crew capsule launcher might be somewhat less likely to fail catastrophically than a bigger liquid fueled rocket (you would want to leave off the SRBs off for the CEV launch, to avoid the potential for another Challenger type disaster). Also, note that we never lost a shuttle or Saturn due to a main engine failure, while we have had an SRB fail.

More importantly, there are many safety factors to consider beyond catastrophic engine failures.

The ability to shut down all engines (can you shut down the SRB stick?) would make ejecting easier/possible in a post-launch emergency.

More net payload to orbit (for 2 launches) can provide a bigger safety margin, both in transit and on the moon.

Once you have a lunar base well equipped, you may want to just send crew directly to the base to rest, load up equipment, refuel, and do a sub-orbital hop to somewhere else on the moon. That sort of mission won't sacrifice payload placed on site, gives the crew a chance to rest (enhancing safety), and decreases the risk of mission failure by reducing the number of launches.

A re-entry capsule with a lower mass to drag ratio (after unloading cargo on the moon and using up most fuel returning) should be safer for re-entry.

More fuel capacity on the CEV at launch could allow aborting a mission from LEO and reduce velocity faster, making emergency re-entry safer and getting the crew down sooner.

FINALLY:
I'm not an "advocate" of Zubrin's approach - I'm just trying to weigh the trade-offs as broadly as possible. I've long been an advocate of separate launch as safer than the all-at-once shuttle approach - but I do think it's worth considering whether that might not be an over-reaction to the shuttle. Zubrin clearly believes that is the case, and he's NOT a stupid guy.

TwinBeam · 2005-08-17 15:01:03

As far as political immunity in 2009, just name the program in honor of JFK - democrats won't dare kill a program that honors Kennedy, and the republican's won't kill it because Bush started it. And it seems kind of fitting anyhow...

GCNRevenger · 2005-08-17 17:05:18

So you are saying that a huge rocket like Magnum will cost the same to launch/fly as The Stick? Thats preposterous, The Stick is a much smaller rocket using the same engines as the big rocket, so why should it? It requires only a third of the mating operations, has a third of the engines, and parts could even be hauled by truck or train instead of barge. I don't think that the launch costs won't be pretty close to proportionate to the parts cost. If The Stick costs a third of the big SDV, then you are talking about spending 50% more money on rockets for every mission.

"...you tend to get what you pay for - even ignoring cost savings from using a larger rocket, you'd still get more payload to orbit in rough proportion to the higher vehicle costs. So Zubrin's approach doesn't have to mean less payload to the moon - just launch one rocket with a CEV and decent payload, and launch another rocket with a fuel tanker..."

Get what you pay for? But you also pay for what you get! You aren't making any sense... it is really very simple: most manned Lunar missions will need only a few tonnes of payload, so it makes much better sense to just send the payload with the crew instead of a dedicated cargo rocket. You don't need twenty tonnes of paylod to send a drill, a rover, or whatnot.

Secondly, to get these few tonnes of payload most efficently, there is an ideal arrangement: one large rocket is simply not large enough but only by 20-30%, and since its hard to put people on a large rocket, then send up the crew on a rocket with 20-30% of the capacity with better safety. To do the opposit is a terrible idea, because it is easier to make a small rocket safe then a big one. Lunar orbit rendezvous is also a proven and relativly safe way to save alot of rocket fuel that would otherwise be needed, as well as offering future upgrade pathes to reuseability that Bob's plan does not have.

"somewhat less likely to fail catastrophically than a bigger liquid fueled rocket"

Compared to the big SDV, three times safer.

You are also all wrong about the Challenger disaster, the SRB didn't fail in such a way that would have killed the crew riding a capsule atop it, the Challenger crew died because there happend to be a tank of liquid hydrogen next to the lowest segment seal. Putting the CEV on the big SDV will present the same exact risk, but putting them on top of an SRB does not, you can have burn through anywhere around any of the seals without a catastrophic failure.

There is this lovely property about large HTPBd solid rockets, that their combustion rate depends on their internal pressure. So, if there were a serious leak, what would happen? The pressure would drop, the combustion rate would drop, and the thrust would fall rapidly. It doesn't need an emergency shut-down, since such behavior is inherint to the engine type. If you really wanted one, you could put explosive punch-outs on the sides of the booster, which would be reliable and effective way to puncture the booster... NASA did invent linear shapped charges you know. Also, the fuel itself is basically a block of rubber, so it cannot crack and shatter like a turbopump can, and the casing is strong solid steel with better structural strength then any other rocket in the world.

Compare the Saturn-V, which only launched a dozen times, to the SRB which has launched over two hundred times, and only failed a single time due to out-of-spec use. Since the Saturn-V had 10-11 and the big SDV has 5-6 large turbopump engines instead of one, your risk of a CATO is multiplied. The big SDV will not have engine-out most likly either for the whole flight regieme unlike Saturn.

"More net payload to orbit (for 2 launches) can provide a bigger safety margin, both in transit and on the moon."

Look, we're not talking a few percent here, the difference between a pair of HLLVs versus one HLLV and The Stick is 57%! Its massively overkill!

"More fuel capacity on the CEV at launch could allow aborting a mission from LEO and reduce velocity faster, making emergency re-entry safer and getting the crew down sooner."

What? The CEV launched on The Stick will carry the fuel needed to return to Earth from Lunar orbit, which is why it will weigh ~30MT, which gives it enough fuel to abort directly back to Earth at any time. As long as the reentry velocity stays at or below trans-Lunar velocity, then the capsule doesn't really care, burning a little extra fuel to reduce reentry velocity way below trans-Lunar doesn't make any sense. The capsule is also going to be a simple thing which will be the same size aproximatly no matter how we choose to get it there.

As far as basing all missions from the Lunar surface, I don't like that idea very much, since we won't have a base for a while, a dedicated "hopper" will be too small, and the crews will get plenty of rest... on Earth!

It is obvious that Zubrin's aproach is short-sighted and a dead end, which is not at all surprising given how he has blatantly lied, hates Moon missions, and is willing to sacrifice a few astronauts to get to Mars just a little faster (putting crew on Ares in MarsDirect too).

Commodore · 2005-08-17 19:22:26

Zubrin does make some points. The need for 2 launches per mission is an added expense, and any hiccup in either launch would seriously screw up the launch windows for the whole mission.

This could be solved by creating as many reuseable compents as possible. The TLI stage could be reused, and fuel for each mission could be launched with the CEV via a EELV, should we choose to go that route. It would certainly make the Air Force happy.

I would perfer the reuseable route anyway. It might be more expensive at first, but unlike the shuttle, stuff left in orbit doesn't require the massive up keep. It would also reduce the investment in production facilities, making ruts a bit easier to get out of.

GCNRevenger · 2005-08-17 20:32:30

It is added trouble, but you get better safety during launch, and by not going direct to the Moon you can take the time on orbit to run diagnostics and see if anything is out of the ordinary before ever leaving LEO, perhaps even release a camera drone or a loop around the vehicle with CEV to check for damage.

Reuseability without Lunar LOX, and I do mean ALOT, does not make any sense at all. NASA can't afford to lug that much rocket fuel, which amounts to much more because now you have to burn fuel for the TLI stage to enter orbit around Earth. It doesn't sound like much at first, but for every tonne you send to the Moon, you need another tonne to get it there, so its actually at least double whatever is required. Reuseing the lander without Lunar fuel is also a non-starter.

The reuseable route would also only be saving the TLI stage, which really just isn't worth very much versus the cost of launching fuel, and since it will double as the upper stage it be "free" so to speak. It can also be simple and cheap, with control/power hardware built into the lander (which will provide attitude control), and only an empty tank with an engine jettisoned after the burn.

Stuff in orbit most certainly does require upkeep, with periodic top-ups of the RCS tankage, regular checks to make sure space debries hasn't punctured it, and making sure the turbopump engines still work after months in the cold soak... oh, and its own retractable solar power supply and remote control link to mission control. Then there is the refueling receptical, which nobody has ever done before with cryogenics in zero-G, and then you have to build tankers...

We already know the route we are taking for CEV, its going to ride on Griffin's favorite, the Thiokol/ATK "Stick." If anything is a done deal, that is.

Ad Astra · 2005-08-17 21:30:54

Zubrin is basically proposing that we return to the Apollo launch mode (single launch on HLLV) but wants to discard Lunar Orbit Rendezvous for direct landing & ascent. That's pretty misguided, considering that NASA was designing the "Nova" rocket (larger than Saturn V) back when direct landing was still a viable option.

I really wouldn't have a problem with launching the crew atop an HLLV as Zubrin proposes, except that I would demand they ride in a small capsule with escape rockets (ala Apollo on the Saturn V.) In all of Zubrin's writings and presentations I have seen, I still don't know where in the Mars Direct hab the crew will sit during launch. I assume they will strap themselves down to their bunks and enjoy the ride. A capsule is the way to go.

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Re: The Case for a Small CEV

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