Un Cev Le Plus Petit Possible

[astroraoul]

Pour retourner sur la Lune, une petite capsule doit suffire! Après tout, le voyage ne dure que 3 jours dans chaque sens...

Voici des fusées qui pourront servir.

 

Voici la lettre de Robert Zubrin à ce sujet:

 

The Case for a Small CEV

Robert Zubrin

Published in the July 4, 2005 issue of Space News

 

There is a strong case to be made for downsizing the Crew Exploration

Vehicle (CEV) into a much smaller, cheaper, and lighter vehicle than

the Orbital Space Plane (OSP) derivatives currently under widespread

discussion.

 

The OSP was conceived of as a means of servicing the crew rotations

of the International Space Station at lower cost and lower risk than

the Space Shuttle. It was thus specified that it be able to carry a

crew of at least five, to approach the Shuttle's crew ferrying

capability. To meet this goal, vehicle masses on the order of 12

tonnes or more were considered acceptable, since the OSP was only

going to orbit, and launch capabilities to deliver such mass to LEO

are readily obtainable.

 

However, now NASA's mission has changed, and instead of perpetual

flights to orbit we are reaching for the Moon and Mars, and the

question must be asked whether such a large crew carrying vehicle

really is optimal to support these new goals. In fact, it is not.

 

The simplest, safest, least expensive, and most capable Lunar base

transportation system is one based upon direct launch to the Lunar

surface, and direct return with no Lunar Orbit Rendezvous (LOR),

using a single launch vehicle. This is so because the direct return

architecture requires the least number of vehicle elements to

develop, expends the fewest hardware elements per flight, has the

fewest necessary operations per mission, avoids the need for untended

mission critical liabilities in Lunar orbit, always has its return

launch window to Earth open, and also has the lowest recurring

mission launch mass once lunar oxygen production commences at the

base. Doing each mission with one launch is also extremely important,

because a multiple launch mission architecture not only costs more,

it greatly increases mission risk. Indeed, a multi-launch Lunar

mission will fail not only if any one of its several launches is

lost, but also if weather or other reasons should cause any launch

after the first to be delayed beyond the boiloff endurance of any of

the cryogenic flight elements launched earlier.

 

This being the case, there is a direct relationship between the

capability of the Heavy Lift Vehicle (HLV) NASA chooses for

development and the allowable mass of the CEV. The fastest route to

creating a HLV at this point is by reconfiguring the hardware of the

Space Shuttle stack, deleting the Orbiter and replacing it with a

fairing and an upper stage. A variety of such Shuttle derived HLVs

are possible, with LEO delivery capabilities ranging from 70 to 130

tonnes, with the more capable versions costing more to develop.

Indications are that NASA has decided to develop such a vehicle, with

the preferred variant in the mid range, offering roughly 100 tonnes

to LEO lift capability. This would be a very reasonable choice.

 

If that is the decision made, then the math that determines

acceptable CEV mass follows directly. Using a hydrogen/oxygen stage

for Trans-Lunar Injection (TLI) and Lunar Orbit Capture, and an

hydrogen/oxygen propelled lander, a system that launches 100 tonnes

to LEO would also be able to deliver 20 tones of payload to the Lunar

surface. If direct return is to be used, this 20 tonnes must include

the CEV plus its ascent stage for flight back to Earth. Using

hydrogen/oxygen propulsion for the ascent stage, an 8.6 tonne CEV

could be thus delivered round trip to the Moon. If instead, for

superior long-term storability, methane/oxygen propulsion is chosen

for ascent, then the CEV capsule would have to be limited to 7.4

tonnes.

 

Such lightweight CEV capsules are certainly possible. For example,

the Apollo capsule, which transported three people to Lunar orbit and

back, had a mass of about 6 tonnes.

 

Thus a lightweight, Apollo capsule derived 3-4 person CEV would allow

a direct return lunar mission with a single launch, but a heavy 5-6

person OSP clone would not. If the heavy OSP clone is chosen, then

development of a Lunar transportation system would require either

development of a second generation super heavy lift booster, an

entire lunar excursion module manned spacecraft system, or

implementation of a costly, complex, and failure prone multi-launch

mission architecture.

 

In short, developing a CEV that is too heavy for the HLV to launch to

the Moon and direct return back would be a huge mistake. If the CEV

matches the direct return mission capability of the HLV, then the

only additional hardware elements needed to begin lunar exploration

are the TLI/LOC stage and the lander. The same lander used to deliver

the CEV and its ascent stage could also deliver heavy cargo such as a

20 tonne habitation module (ISS modules weigh 20 tonnes), making long

duration lunar surface stays possible right from the start of the

program.

 

But the small CEV not only cheapens and accelerates the Lunar

program, it cheapens and accelerates the CEV program itself. The

funds saved by reducing the size and cost of the CEV could be used to

start HLV development immediately, which would save further funds,

since early deployment of the HLV would allow space station

construction to be completed sooner, allowing early retirement of the

$4 billion per year Space Shuttle.

 

By reducing the size of the CEV to close derivative of the Apollo

capsule, the CEV program could be turned from an extended

developmental contractor banquet into a production procurement. With

development minimized, NASA could compete a contract of the following

form: "The winner of this contract will be paid $300 million each for

five CEVs if they are delivered in 2008, plus $200 million each for

five CEVs delivered in 2009, and $100 million each for five CEVs

delivered per year starting in 2010 through 2015." Such a contract

form would provide a strong incentive for early delivery of the CEV,

thereby allowing early retirement of the Space Shuttle without any

discontinuity of US human spaceflight capability. Furthermore, it

would eliminate nearly all NASA expenditure on the CEV program during

2006 and 2007, allowing these funds to be reprogrammed for immediate

development of the HLV. Together with other savings obtained by

canceling useless programs such as the Hubble deorbit module, these

funds should be sufficient to pay for the entire HLV development.

 

So to summarize, the choice of small CEV enables an optimum single-

launch, direct-return, Lunar mission architecture. It also enables a

reduced cost, accelerated commercial procurement of the CEV itself.

The savings in the CEV program thus obtained can be used to launch

the HLV program immediately, and together the CEV and HLV would allow

early retirement of the Space Shuttle, with massive savings to the

taxpayer resulting.

 

Furthermore, with a CEV matched to an HLV for direct lunar missions

in hand, and STS retired or nearly so, outgoing NASA Administrator

Griffin would be able to say to the President elect in January

2009: "We have 80% of the hardware needed for human lunar missions

already developed, and have freed the funds required to develop the

rest. If you choose to go forward with flat funding, we can have

humans on the Moon by 2012, and Mars by 2016, by the end of your

second term. The choice is yours."

 

It's a winning pitch.

 

Dr. Robert Zubrin, an astronautical engineer is president of the Mars

Society and author of The Case for Mars (Simon and Schuster 1996),

Entering Space (Tarcher Putnam 1999) and Mars on Earth (Tarcher

Penguin 2003).

 

 

Songeons un peu: une capsule surmontant une fusée: on pourra d'abord tester la fusée en la surmontant d'une maquette; puis on pourra tester la capsule vide, puis on testera la capsule avec un astronaute à bord mais avec la petite fusée pour l'orbite terrestre. La capsule sera surmontée d'une tourelle d'éjection.

Rien de tout cela n'a pu être possible avec la Navette: Tout a été testé d'un coup, avec Young et Crippen à bord. Une navette placée le long du réservoir et à côté des propulseurs d'appoints, sans tourelle d'éjection et avec la promesse que le risque d'accident fatal serait d'un vol sur 10.000...

 

Raoul

[lambda0]

Toujours très pertinent ce Zubrin.

On se demandait pourquoi en 2015, il faudrait assembler un vaisseau lunaire en orbite au moyen de plusieurs tirs, alors que dans les années 1960, on y allait directement.

Mais, bon, il me semble bien que le CEV n'est toujours qu'à l'état de projet, ça peut encore évoluer.

[ulysse31]

http://www.marssociety.de/emc/proceedings/Ferra.pdf

 

On peut rêver non?

[PVG]

Bonsoir à toutes et à tous et à Astroraoul en particulier (j'espère qu'Alphonse ne en voudrait pas de surfer sur d'autres sites).

Les Européens voulaient faire une navette "Hermès", nous avons fait une capsule l'ARD (démonstrateur de rentrer dans l'atmosphère style Apollo) essai réussi, nous avons construit Columbus mais c'est une navette qui doit l'envoyer, le CRV est presque prêt mais nous n'avons pas d'accès autonome pour nos Astronautes à ISS qui nous coûte pas mal d'Euros. Alors pour allé sur la Lune !!! et Hubble Space Telescope nous y avons participé aussi. Bon je vais me coucher.

A + PVG

[astroraoul]

Salut Philippe!

Dans les années 60, les journalistes ne se sentaient pas concernés par combien cela coûterait et puis après, chaque mission commence par : cela coûte autant....sans vraiment s'intéresser à la science derrière.

 

Raoul

[titeuf16]

Salut je pense qu'il fau mieux envoyé un petit vaisseaux que peu se deplacer plus rapidement qu'un grand et en plus cela coutera moin cher

[lolomalin]

Pour poursuivre, je pense que l'idéal est aussi dans des vaisseaux petits, donc maniables, plus sûr.

il faut plutôt s'interesser à des lancements en kit avec de petits lanceurs qu'à des vaisseaux énormes, pour faire des lancements interplanétaires

[Yantar]

Pour ma part, le vaisseau idéal serait multi fonction. Je vois bien un module de propulsion genre Centaur amélioré, surmonté d'un module d'habitation et au sommet, soit une petite navette type X-38 ou une capsule type Apollo. L'avantage d'un dérivé du X-38, ce serait un retour sur Terre moins brusque, ce qui serait un plus si on revient de la Lune ou de Mars. L'engin serait lourd. Mais il existe déjà la solution à celà. Le système propulsif du shuttle est le pluis puissant au monde. Il suffit de voir la navette qui pèse 70 tonnes et peut transporter 20 à 30 tonnes selon l'orbite visée. Moyennant quelques aménagements, on a le lanceur. Il a prouvé sa fiabilité puisque en 113 lancements, il n'y a eu qu'un seul accident. Pourquoi développer un lanceur super puissant alors qu'on a déjà quelque chose de très performant et qui peut encore être amélioré...