The Case for a Small CEV

idiom · 2005-08-18 01:05:55

If the crew was launched after the BDB in something likle the T/Space design then weather and capsule problems wouldn't be an issue. Does anybody know what Zubrin's position on T/Space is?

GCNRevenger · 2005-08-18 08:48:30

Yeah, Bob's idea of putting the crew in the MarsDirect HAB with no option for escape is stupid, and one of the big reasons I think he isn't too concerned with losing a few men to get his boots red a little quicker. Its hurt his credibility with me.

If its any position besides "highly skeptical" then Bob is crazy... a half-billion dollar price tag to a company that has only made that dinky oxymoronic "SpaceShipOne" with 1/25th of the money, and they want to go orbital? Thats something of a risky proposition.

Ad Astra · 2005-08-18 19:51:47

Not to mention that t/Space's air launch method squanders the release velocity and doesn't take advantage of the reduced gravity losses inherent in winged vehicles.

TwinBeam · 2005-08-18 20:18:51

GCNR:

I didn't say a Magnum would cost the same to launch as The Stick - but you can't ignore support and fixed overhead costs. E.g. two Stick CEV launches probably cost more than one Magnum launch, once all costs are added in. I also didn't say the SRB failed catastrophically - just that it failed. Any engine failure puts crew at risk.

Safety has to be considered from a whole mission perspective. The chance of any engine failure is small enough that the difference in safety between 1 and 3 engines is small compared to whole mission risks - certainly under 0.5% for either approach, probably lower.

Yes, you pay for what you get in terms of mass - but so what? The "base+hopping" approach means you don't take redundant equipment mass and leave it scattered all over the moon. Less net mass is required over multiple missions, so you end up paying less for the same level of capability. You also wouldn't have the redundant mass of a CEV and separate LSAM, as those are merged, with the CEV serving as ascent module.

But, as I said, I'm just considering options - I'm not religiously devoted to a particular mission profile. If SRBs save on maintenance and support (e.g. no cryogenics) for their level of capability and safety, why not build the entire first stage architecture around them? Use a bundle of 6 SRBs instead of the ET derived first stage that needs 2 SRBs anyhow. Maybe get some economies of scale on the SRBs.

GCNRevenger · 2005-08-18 21:00:13

Your assertion that The Stick will cost very disproportionatly more in non-hardware costs to fly is unfounded, since most of the non-hardware cost goes to assembling the hardware. Less hardware, less non-hardware costs... In fact, The Stick could be assembled at the launch pad, skipping the VAB/crawler entirely.

Not all engine failures are created equal, a burnthrough on an SRB is a pretty graceful failure, just losing thrust and having to abort, but having a turbopump on an SSME come apart would mean instant Challenger-like destruction.

If you don't need 57% extra payload to carry out a Lunar mission, does it not make sense to reduce the mission price by 50% as well as improving the safety by launching the crew on The Stick?

The Base/Hopping aproach isn't very good for a few reasons:

~There isn't going to be a Lunar base for fuel for many years, which is years delaying gainful exploration until it is online.

~Limits where you can go, since a trip far from base would take almost as much fuel as entering Lunar orbit and any trip would involve TWO powerd launches/landings instead of one.

~Hopper cannot provide signifigant time at a location without carrying an LSAM-sized crew cabin and life support supplies. Add this, the payload, and the extra fuel and the vehicle starts getting big (and expensive) quickly.

~Dedicated LSAM gives the crew "free" backup life support just like Apollo-13, improving safety over just CEV.

NASA considerd such a route with making a massive all-solid first stage for its NOVA rockets, but since the upper stage will definatly not be that big, this won't be very practical. Such an arrangement is not very efficient either, where on Shuttle you get the average of the high Hydrogen performance and the low solid rocket performance during launch, instead of just the low-Isp solid rockets.

idiom · 2005-08-19 18:59:45

The bit about T/space wasn't about T/Space pre se, it was about the flexibility of their launch system. There exists an arugment that launching the crew can be fiddly and might go past the Mega-launch boil-off point as it waits on orbit. T/Space can launch around weather and keep several capsules on hand, thus increasing the reliability of the second launch.

srmeaney · 2005-08-20 00:47:56

They need a single stage vehicle that moves fifty passengers from the earth to the Moon and back again without fail. Wasting time and resources on building stuff that burns on re-entry every launch is not the better option.

TwinBeam · 2005-08-20 03:13:33

Your assertion that The Stick will cost very disproportionatly more in non-hardware costs to fly is unfounded, since most of the non-hardware cost goes to assembling the hardware. Less hardware, less non-hardware costs... In fact, The Stick could be assembled at the launch pad, skipping the VAB/crawler entirely.

Hmm - how about all the small army of highly trained people kept on payroll all year to handle a few moon missions a year?

If you don't need 57% extra payload to carry out a Lunar mission, does it not make sense to reduce the mission price by 50% as well as improving the safety by launching the crew on The Stick?

What extra payload? For a single-launch mission, there's no excess payload. For a dual launch, the second launch could be entirely fuel, allowing you to get more useful payload launched with the crew, and if you have extra fuel from that mission, leave it in orbit or on the moon for future use. Use whatever mix of the two mission profiles to get exactly the amount of payload and fuel you want.

The Base/Hopping aproach isn't very good for a few reasons:
~There isn't going to be a Lunar base for fuel for many years, which is years delaying gainful exploration until it is online.

I don't see the difficulty - land a tanker with whatever you can get there, set up a solar panel, plug in the cryogenic cooler to keep the O2 below boiling. Use methane for fuel so you don't need to deal with extremely low temps of liquid H2. That's enough to serve as the core of a base - perhaps "fuel dump/equipment store" is more accurate.

~Limits where you can go, since a trip far from base would take almost as much fuel as entering Lunar orbit and any trip would involve TWO powerd launches/landings instead of one.
~Hopper cannot provide signifigant time at a location without carrying an LSAM-sized crew cabin and life support supplies. Add this, the payload, and the extra fuel and the vehicle starts getting big (and expensive) quickly.

Actually, three launch/landings- (land, hop out, hop back, return) but so what? Moving a rover or other equipment from a base to anywhere on the moon will take FAR less fuel than bringing the same equipment up from Earth for every different spot you want to visit. If you find it useful to stay longer at a site, sure, go ahead and set up the equivalent of an inflatable tent and an air recycler of some kind.

~Dedicated LSAM gives the crew "free" backup life support just like Apollo-13, improving safety over just CEV.

It's hardly free if you have to lug it's mass with you all the way from Earth's surface, every flight. It would seem just as easy and less net mass to carry double the O2 you think you'll need for breathing, and to have a CEV ready to launch on a rescue mission - maybe already in orbit even, since it wouldn't need to have a crew.

NASA considerd such a route with making a massive all-solid first stage for its NOVA rockets, but since the upper stage will definatly not be that big, this won't be very practical. Such an arrangement is not very efficient either, where on Shuttle you get the average of the high Hydrogen performance and the low solid rocket performance during launch, instead of just the low-Isp solid rockets.

True, not very efficient - but if they get the same job done for less money, I doubt we'd care if they use more fuel.

GCNRevenger · 2005-08-20 06:57:55

You size your work force to meet the launch demands. If you only need few sticks and three or four magnums per year, then thats all you have personell to build & fly.

"What extra payload? For a single-launch mission, there's no excess payload."

Are you even listening to me? Let me give you the bullet points:
-All missions to the Moon will require several tonnes of payload (drills, telescopes, rovers, 6mo supplies, extended LSS, etc). Not tens of tonnes, but only a few. More payload then this is unessesarry and expensive.
-Direct flight with any affordable HLLV, despite hydrogen engines, cannot carry any payload, and can only just barely get a minimal crew capsule back to Earth
-Therefore, a seperate cargo launch would be required to carry this payload or the fuel to move it. NASA's current plan is to address this issue by launching the crew seperatly on a smaller rocket (optimized for safety to boot) and use the Lunar-rendezvous mission plan to save on fuel. You wanted to use an HLLV for this second cargo flight!

Look, it ain't rocket science... when you send a crew to the Moon via direct flight, no matter what they are going there to do, they are going to need a few tonnes of stuff. ONLY a few tonnes. So why WOULDN'T you send the payload with them? To get these few tonnes, you are going to have to launch a second rocket, so why WOULDN'T you put the crew on it??? No other mission plan makes any sense!

If we are going to have a Moon base, which seems to be a major VSE goal, then that base is going to need a crew rotation every six months or so. Missions to sites of interest distant from the base will have to be accomplished with their own missions too, probobly like one anually. Minimizing the price per-mission is essential if we are to have any money left to think about Mars, then sending two HLLVs is wasted money that could have gone to other things.

"I don't see the difficulty - land a tanker with whatever you can get there, set up a solar panel, plug in the cryogenic cooler to keep the O2 below boiling"

Wrong! A hopper mission of the size required would use up so much fuel, that a huge HLLV tanker like you have described would be mostly used up in a single long hop! Its not any cheaper to send the fuel to the Lunar surface then it is use it from Lunar orbit. The hopper plan doesn't make any sense unless Lunar oxygen is available. Period, end quote.

"but so what? Moving a rover or other equipment from a base to anywhere on the moon will take FAR less fuel than bringing the same equipment up from Earth for every different spot you want to visit. If you find it useful to stay longer at a site, sure, go ahead and set up the equivalent of an inflatable tent and an air recycler of some kind."

Wrong again... the Moon is a BIG place, seven thousand miles around the circumferance, and we're still trying to figure out how to make a rover with a range of 500mi. The best place for telescopes is on the dark side, missions to the Lunar poles would be of great interest, and there are impact craters worth visiting all over the Lunar surface. And thats as the crow flies, and not the winding out-of-the-way path needed to get to your destination... if you can get there at all. How do you drive into a crater with sheer walls, or up a moutain with no convienant switchbacks?

A rover isn't going to do you much good. It actually will cost less fuel and trouble to send the missions from Earth.

"and an air recycler of some kind."

Heavy, energy-hungry, a little bulky, and doesn't make gasses to refill the airlock nor does it make power during Lunar night or in a shadowed crater.

"It's hardly free if you have to lug it's mass with you all the way from Earth's surface, every flight. It would seem just as easy and less net mass to carry double the O2 you think you'll need for breathing, and to have a CEV ready to launch on a rescue mission - maybe already in orbit even"

Which is more then made up for by the improved fuel efficiency of Lunar orbit redezvous instead of direct return. It takes about twenty tonnes of propellant to get the CEV capsule home again (NASA wants Methane probobly), and not lugging this off the surface like Bob wants makes a HUGE difference.

And Bob wants a direct flight mission with Hydrogen fuel, you CAN'T park it in orbit for an emergency. It needs every single gram of fuel just to get home, and you would have to burn some fuel just to circularize your orbit around Earth or the Moon. Fuel you can't afford... Furthermore, Bob's rocket MUST use hydrogen fuel, or else it is too heavy to make the round trip using any of the SDV HLLV rockets. If you were to park this vehicle in orbit for months, or store it on the Moon for a six month crew rotation (!!!), this fuel would be alllllllllll gone.

Bob's plan is a one-way ticket to doing Apollo over again, and quitting the Moon after we went through so much trouble, and despite that there is much to learn and to gain from the Moon, all sacrificed in a mad, blind rush to get to Mars.

srmeaney · 2005-08-20 19:22:39

Are you even listening to me? Let me give you the bullet points:
-All missions to the Moon will require several tonnes of payload (drills, telescopes, rovers, 6mo supplies, extended LSS, etc). Not tens of tonnes, but only a few. More payload then this is unessesarry and expensive.

I think the idea is fill the extra space with tourists and/or private sector crew. Standardise large capacity payloads and fill to that capacity. Not only does a standardised payload capacity vehicle reduce long term costs, it must ultimately allow for cheaper space access for non government exploration and colonization. If you can fit the extra tourist to the moon and a couple of little private sector mining rovers that scoop soil and extrude bricks, let it happen... It can only be of benifit.

They are only keeping it Government and small because they dont want some tourist who isnt a signatory to the UN kicking out a camcorder broadcast unit and flag and going "I claim this Moon in the Name of Norway!"

And Bob wants a direct flight mission with Hydrogen fuel, you CAN'T park it in orbit for an emergency. It needs every single gram of fuel just to get home, and you would have to burn some fuel just to circularize your orbit around Earth or the Moon. Fuel you can't afford... Furthermore, Bob's rocket MUST use hydrogen fuel, or else it is too heavy to make the round trip using any of the SDV HLLV rockets. If you were to park this vehicle in orbit for months, or store it on the Moon for a six month crew rotation (!!!), this fuel would be alllllllllll gone.

Incorrect. Store it as water and seperate fuel components just prior to launch.

GCNRevenger · 2005-08-21 01:23:11

Soooo you would bet the fuel for your ticket home on a electrolosys unit that you don't have any payload mass to carry, no power source to operate, and have to avoid the frozen water from expanding and ruining your fuel tanks/lines for 6mo even though you have 400F degree swings every month between Lunar night/day.

Me, i'll stick with LOX and liquid Methane.

TwinBeam · 2005-08-21 03:50:10

GCNR

You ask if I'm listening to you, but with all your SHOUTING , I don't think you're really hearing what I'm saying.

Let me see if I can make it simpler...

Launch one tanker to LEO. Launch another to lunar orbit. Launch one to a first moon base site. (Not that this is an optimal approach, but it's hopefully simple enough so you'll see my point.) Assume the tankers carry methand and O2, so they can stay parked up there for a reasonably long period..

Now - how big should your first crewed mission be? You want to send 3 astronauts and just a few tons of equipment? Fine - load it up. Now load up the rest of your payload mass as fuel. Ooops - not enough fuel to get there and back? Well, aren't we lucky - we've got fuel sitting in several convenient places, ready to collect and use. So we've got EXACTLY the payload we want to send, and we use EXACTLY as much fuel as it takes - and the other fuel we sent up that doesn't get used isn't wasted - it will just get used in a later mission. Don't want to lug fuel down to the moon's surface and back up again for the return to Earth? Great! Just rendezvous with the tanker in lunar orbit after ascent from the moon, to take on the fuel you need to get home.

RE: the rover - you've misunderstood again. I am not talking about having a rover that drives hundreds of kilometers. I'm saying that if you have lots of missions that require a rover, you don't want to send a new rover all the way from Earth for every different site you're going to explore. Instead, you want to deliver one rover to your base. Then for missions that need a rover, you go to the base first, load the rover onto the the lander (which is how the rover got there in the first place - perhaps on an automated "cargo only" version). Then you load up sufficient fuel and supplies for a hop to the exploration area and back. And off you go.

Is this cheaper than sending a rover down from lunar orbit? No, not the first time. Maybe not even the second time, despite not having to bring a rover up from Earth. But by the 3rd such mission, the savings of not bringing a new rover up from Earth, and abandoning it at the end of the mission, will more than make up for the extra fuel expended in the hops to deliver it and bring it back to base.

GCNRevenger · 2005-08-22 18:16:04

"Launch one tanker to LEO. Launch another to lunar orbit. Launch one to a first moon base site"

Tankers are basically tugs (with cryogen coolers?), which don't come cheap, and neither do landers, which you have now added several of to an otherwise simple arcitecture. Also, each of those tankers would each need their own launch vehicle, and as history and basic engineering show us that multiple smaller rockets are more expensive then fewer larger rockets. Then there is the probability that one tanker will fail, and delay the whole mission. Having tugs also doesn't change how much fuel you need, it just changes how it gets there! And in this case, its a change for the worse versus the "reference mission" NASA has in mind.

"You want to send 3 astronauts"

No, four astronauts for surface stays of about two weeks, or six for base crew rotations without extended life support. The lander should also carry a few tonnes of payload as well.

The savings of not having to bother with the tankers would more then make up for building a copy of a rover, I think.

SpaceNut · 2005-08-23 10:39:52

Well since this thread has talked about why a small cev is not in the best interest fun use for going to the moon. [url=http://www.flightinternational.com/Articles/2005/08/23/201125/+NASA+picks+rocket+for+return+to+Moon++.html]NASA picks rocket for return to Moon
Agency opts for 100t launcher using Shuttle technology.[/url]

Well not much of an exclusive:

NASA has decided to develop a 100t to low-Earth orbit (LEO) in-line heavylift booster using a highly modified external tank and new five segment solid-rocket boosters (SRB), Christopher Shank, special assistant to NASA administrator Michael Griffin, has revealed to Flight International.

What based the direction of the HLV:

A lot of this decision has to do with launch loads and safety aspects. It is better to do it with in-line,” says Shank.
He adds that NASA’s leadership is aware that an in-line booster requires major launch complex and vehicle assembly building changes, but future budget estimates take this into account. Planners are working on the 2007 budget. Shank expects US congressional representatives will want to discuss the decision when they reconvene on 9 September.

Why the shuttle -c was not in the running:

The alternative to the in-line version was an expendable 70t-to-LEO side mounted Shuttle-like cargo pod. However, the 5 August selection of the in-line solution was based on work carried out by the 60-day Exploration Systems Architecture Study (ESAS), created on 29 April by Griffin, and earlier studies that fed into ESAS.

What can we expect for the LEO CEV or spiral 1:

ESAS concluded that the CEV launcher should have a 35t-to-LEO capability because two CEV versions are needed: a 25t International Space Station crew transfer variant and a 35t lunar mission CEV.

Ad Astra · 2005-08-23 18:17:05

Sanity is on the march down the halls of NASA.

I'm glad that the agency is spending money upfront to build the SDLV correctly instead of cheaping out and getting a Shuttle-C knockoff that doesn't leave room for growth. The in-line SDLV won't be a true clean-sheet design, but with all of the necessary changes, only the SRB's will look remotely like the ones on the Shuttle.

Because NASA needs to rebuild the crawlers to support SDLV, I wonder if NASA will refurbish the third crawler from the Apollo days, which has been rusting away in a field. My experiences in Florida tell me that 30 years of Florida humidity have not been kind to it. If it's not going to be fixed, it would be possible to use one crawler for Stick launches while the other one is being redesigned.

TwinBeam · 2005-08-23 18:35:09

"Launch one tanker to LEO. Launch another to lunar orbit. Launch one to a first moon base site"
Tankers are basically tugs (with cryogen coolers?), which don't come cheap, and neither do landers, which you have now added several of to an otherwise simple arcitecture. Also, each of those tankers would each need their own launch vehicle, and as history and basic engineering show us that multiple smaller rockets are more expensive then fewer larger rockets. Then there is the probability that one tanker will fail, and delay the whole mission. Having tugs also doesn't change how much fuel you need, it just changes how it gets there! And in this case, its a change for the worse versus the "reference mission" NASA has in mind.
"You want to send 3 astronauts"
No, four astronauts for surface stays of about two weeks, or six for base crew rotations without extended life support. The lander should also carry a few tonnes of payload as well.
The savings of not having to bother with the tankers would more then make up for building a copy of a rover, I think.

Still not reading what I wrote... I wrote that launching a bunch of tankers and then the crew was not a realistic mission profile. It was an exaggerated explanation of why there would never be any "excess" payload or payload capacity going un-used, regardless of mission configuration.

Any "excess" fuel is left parked in space, where it'll eventually be useful for some later mission - so we don't need to launch a tanker for every CEV mission. Every crew or cargo mission can be exactly "right-sized" for its objectives, with fuel from the tanker used as necessary to make the mission work.

One would initially put one tanker in lunar orbit, to provide the greatest flexibility and mission safety. Since tankers are launched independent of any CEV mission, there's plenty of time to deal with the rare case that a tanker fails. Mission delays are far less likely than with the Stick and Magnum paired-launch scheme.

Why did you think the tanker requires a smaller launch vehicle? It'd use the exact same big launch vehicle as the CEV-lander, and the same lunar insertion stage. It'd just replace the CEV-lander with methane/O2 tanks and a cryogenic cooler for the O2.

Since early tanker missions would only go to lunar orbit, no extra landers are needed. When landing a tanker on the moon becomes desirable, an automated cargo-only lander mission - which we'll need for other deliveries - would simply carry a tank of fuel as cargo. Hopefully by that time O2 production will be in operation, so all you need to deliver is fuel.

If it was eventually decided to put a tanker in LEO, the lunar insertion stage would still be used to get into LEO, but with methane for fuel. The methane and O2 of the barely-used insertion stage can provide additional tanker capacity.

Three astronauts was also just an example - four or more would work just as well. That's the point - this approach offers the flexibility to exactly right-size each and every mission, trading off crew/cargo/fuel on the CEV for fuel from tankers.

TwinBeam · 2005-08-23 18:56:05

I do like the "Stick" for crew launch, if they're just going to LEO, e.g. to the ISS.

If we eventually start using a re-usable lunar ferry and re-usable lunar orbit-to-surface ferry, it'd make a lot of sense to bring crew up on a Stick. But I think that'll have to wait for lunar O2 to get into production, as otherwise we waste a lot of fuel lugging the ferry and it's Earth-return methane/O2 to the moon and back. If we ony have to haul the ferry and its methane, and since we also no longer need to haul a new lunar insertion vehicle and LSAM up from Earth every time, we should at least break even.

In the meantime, wouldn't it be smarter to develop just one new, flexible launch system, instead of two very different vehicles that must BOTH work as planned, or neither is of much use for the moon?

Going to a linear configuration and getting rid of the tiles and using a better re-entry vehicle will eliminate a lot of the Shuttle's dangers. If safety is still a concern, launch the CEV without SRBs, and launch fuel tankers with four SRBs, to put more fuel in space per launch. More fuel in space means we need less fuel on the CEV, allowing us to keep the payload capacity we need.

RobertDyck · 2005-08-23 19:14:36

The Moon has no atomsphere so you can't aerobrake. Using fuel to enter orbit then more fuel to de-orbit and land would take more fuel than just to land directly. If you want a lunar shuttle it should go from lunar surface to Earth orbit.

John Creighton · 2005-08-23 20:00:38

The Moon has no atomsphere so you can't aerobrake. Using fuel to enter orbit then more fuel to de-orbit and land would take more fuel than just to land directly. If you want a lunar shuttle it should go from lunar surface to Earth orbit.

Have you done the calculations for either way of exploring the moon? I suppose it should take less energy to reach the moon then circularize as you could use the moons gravity to pull you in past the L point. But then you have to hall that ship back off the surface again. Maybe lunar fuel could make the difference.

I am thinking of something here. If cargo is hulled in a second vehicle then the vehicle built to hull the cargo does not have to be hulled back to earth. Perhaps a bigger CEV would have wasted empty space for the return flight home. As a compromise how about a light CEV with an expendable cargo pod that we leave on the moon. That way we get the extra cargo benefits of a bigger CEV, will not be wasting the capacity of the solid boosters and would have a light lunar mission option should we ever need or desire it.

John Creighton · 2005-08-23 20:13:27

I’m a little mixed up here. The CEV doesn’t even land on the moon right? The CEV is for earth reentry and the lunar Lander lands on the moon? Or do I have that wrong? Anyway if the CEV is separate from the lunar lender extra weight in the CEV would seem wasted as it would go know where. Also if the Lander was separate the cargo pod could fit between the lunar Lander and CEV. If the Lander was reusable then on subsequent missions the cargo pod could be made bigger as the Lander wouldn’t have to be pushed to the moon again. Complete reusability wouldn’t even be required reducing the amount of Landers that have to be pushed to the moon by any number will be a saving. If lunar fuel wasn’t available perhaps the cargo pod could have a fuel tank until lunar fuel became available.

Ad Astra · 2005-08-23 22:40:32

John:

As currently envisioned, CEV is like the Apollo CSM and the LSAM is like the LEM. Aside from the fact that the CEV launches on a different rocket than the LSAM, it's the same mission architecture as Apollo.

It might be possible at some time in the future to make a reusable LSAM and reusable CEV. The current plan is to reuse the CEV on ISS missions, but to discard it after moon missions. The reason is because the heat shield ablates less when returning from LEO versus returning from the moon. The heat shield that can survive one lunar reentry will survive 10 ISS re-entries, in theory.

RobertDyck · 2005-08-23 23:10:11

Think of it this way. If you parked in highly eliptical orbit around the Moon before descending to land, then de-orbited for landing the fuel spent would be the same as if you directly land. But circularizing orbit wastes fuel to lower the apolune. Parking the "mother ship" in lunar orbit was beneficial for Apollo because:
1) only a small portion of vehicle weight landed, the LM was lighter than the CSM
2) low Isp fuel (UDMH & N2O4)
3) the LM was expendable
4) no use of lunar oxygen

Actually use of lunar oxygen as propellant completely changes everything. If you use either LH2 or methane, producing oxygen to lift off the Moon alters the weight so much that you're much better off with a single vehicle that lands. Robert Zubrin presented this at the 2004 convention in Chicago.

The Apollo LM was made of aluminum so thin it would only withstand 5 pressurization cycles. An astronaut said in a TV interview that it was 5 times the thickness of Renolds aluminum foil, the kind you use in the kitchen. If they dropped a screwdriver tip down it would puncture the pressure hull. You want something more robust this time. If you want more than a flags and footprints mission it will have to handle more than 5 pressure cycles. A heavy pressure hull again leans toward a common hull for transit and the surface of the Moon.

John Creighton · 2005-08-23 23:48:49

If circularization is such a problem would it be possible to detach from the CEV in an elliptical orbit and then land on the moon. As for docking after taking off from the moon perhaps the CEV could still be in an elpitical orbit or maybe some ballistic capture could be done to circularize the orbit exploiting the 3 body problem.

John Creighton · 2005-08-24 01:03:21

I'm not sure if it takes much more energy to circularize then land directly. As long as you fire all engines in the opposite direction you are traveling then all energy is used to slow down and none is used to change direction. There are the gravitational loses which I am trying to understand. I think it has to do with how work is equal to force times distance. So if you fire your engines while you are moving faster you are going to do more work since the force remains constant. So I would think you could reduce gravitational loses by landing directly. However, if you slow down earlier the vehicle will be lighter and the gravity won't give it as much momentum.

When taking off from earth both of these factors work against a low thrust vehicle. When landing they cancel each other out some so I am not sure how it comes out. If the vehicle weighs much more then the fuel you clear want to land as fast as possible. But if the fuel makes up a significant fraction of the vehicle I don't know if this is true any more.

SpaceNut · 2005-08-24 05:45:17

I wonder if NASA will refurbish the third crawler from the Apollo days, which has been rusting away in a field.

Not likely since they need to replace bearings in one of the currently used units a few years back, to which I am sure they have taken anything that is still of value from it has been raded from it.

John Creighton's question of RobertDyck comes down to this I think:
Circularization of orbit does a couple of things if we have brought the CEV along like apollo did, it slows the combined unit down to lunar orbit and relaunch speeds for recapture when ready to return to Earth it also gives a semi stable place to park the CEV and allows for a slow descent to lunar surface, which was need for the old LM being so thin walled. It also makes it easier for the LSAM to recapture for return too, which may be need if LSAM vehicle is a methane powered.

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#38 2005-08-22 18:16:04

Re: The Case for a Small CEV

#39 2005-08-23 10:39:52

Re: The Case for a Small CEV

#40 2005-08-23 18:17:05

Re: The Case for a Small CEV

#41 2005-08-23 18:35:09

Re: The Case for a Small CEV

#42 2005-08-23 18:56:05

Re: The Case for a Small CEV

#43 2005-08-23 19:14:36

Re: The Case for a Small CEV

#44 2005-08-23 20:00:38

Re: The Case for a Small CEV

#45 2005-08-23 20:13:27

Re: The Case for a Small CEV

#46 2005-08-23 22:40:32

Re: The Case for a Small CEV

#47 2005-08-23 23:10:11

Re: The Case for a Small CEV

#48 2005-08-23 23:48:49

Re: The Case for a Small CEV

#49 2005-08-24 01:03:21

Re: The Case for a Small CEV

#50 2005-08-24 05:45:17

Re: The Case for a Small CEV

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