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What are the reasons...

Posted by: Ekkehard Augustin - Tue Sep 20, 2005 11:14 am
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What are the reasons... 
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Post    Posted on: Fri Sep 23, 2005 7:14 pm
SawSS1Jun21 wrote:
I have reflected upon this for some time now and I am beginning to suspect that the "re-usable" specification of the upper stages of Falcons V and IX (the upper stage of I is NOT re-usable) is probably lip service to Bigelow.


That, or a way to win some orbital prize if some requirement is made to re-use the booster. He can always omit the chute or say it was meant to be deformed upon crashing. Sea Water and electronics don't mix well. With rugged pressure-feds, you might get away with sea-recovery and be all right.

The first Falcon flight now moved to October due to yet more engine headaches.


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Post    Posted on: Fri Sep 30, 2005 8:51 am
To point to the different kinds of reusability that could be appliedhere again:

The Earth Departure Stage could be kept in space for its complete lifetime. In that case it only would be required to let it return into orbit only - instead of reentry and landing.

The propellant had to be delivered then only - which could be done by several flights which deliver other cargo too. The "other cargo" may be for the ISS for example. That could be a task for t/Space who already have proposed tankers in their CEV concept - or it could be done a way described int the thread about tankers and alternatives for tankers.

The longer crews stay on moon the more advantageous such an approach would be or become.

The Earth Departure Stage would require an additional amount of propellant for turning back to Erath and for orbit insertion then. Alternatively it could be carried by the CEV to the moon and then back into Earth orbit.



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Post    Posted on: Tue Oct 04, 2005 10:15 am
Regarding the possibility to switch over to a SpaceX's reusability-technology NASA's schedule seems to include the opportunity to do such a switch. The article "NASA Propulsion Strategy Reaches Back While Looking Ahead" ( www.space.com/spacenews/businessmonday_051003.html ) says
Quote:
The heavy-lift rocket, which NASA intends to start developing around 2011
.

SpaceX intend to have ready their fully reusable rockets in 2008 - so there is a chance that they have ready their reusability-technology before NASA start the development of the heavy lift rocket.



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Post    Posted on: Wed Oct 05, 2005 9:45 pm
Heavy Lift really mean 100 tons to orbit. Falcon IX puts 22 in LEO at most. That should be called medium lift.


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Post    Posted on: Thu Oct 06, 2005 11:19 am
There is another thought I had just this moment. I was asking why NASA don't involve the idea to make use of SpaceX's reusability-technology and the answers and informations provide acceptable answers to a high degree.

But regarding the reusability of the lander the answer is worth to be extended. It is obvious that NASA will do several landings on the Moon and not only five within five years. They want to build establish and permanently keep manned a lunar station.

Und these condiations the lander could be reusable an easy way - they simply could install a space station in a lunar orbit to which the lander is docked when no crew is down on the surface. There is no atmosphere and so no reentry.

That lunar space station could be kept small compared to the ISS, the Skylab or Mir since it would be designed to transit from a CEV to the lander only. Perhaps the possibility should kept to enhance that small space station for docking more than one lander or more than one CEV to it.

Doing so might have another advantage too - it wouldn't be required to carry a lander from Earth to Moon each mission. This could save propellant once the lunar space station is installed. So what about this? Is there a problem - except the additional initial transportation, installation and construction costs (Bigelow could build it)?



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Post    Posted on: Thu Oct 06, 2005 6:20 pm
Falcon is not going to be reusable for long. My guess is they will recover a few boosters, and then decide to just stage them off and forget them as being more trouble than it is worth to recover. The Bat approach of Orion Propulsion is more of a true reusable.

By Musks definition, even the R-7 is reusable because they take parts off the crashed strap-ons away with them before leaving the builk of the tankage behind for the Kazakhs to make tools and sheds out of. I doubt that Musk will be doing much more than that.


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Post    Posted on: Fri Oct 07, 2005 11:22 am
The article "The Mega-Module Path to Space Exploration (Or: How to Use an HLV)
" ( www.space.com/adastra/adastra_mega-modules_051007.html ) says
Quote:
The 60-day report indicates that an expendable trans-lunar stage would be used for lunar expeditions. There is no reason why this stage could not be re-designed into a re-usable Cis-lunar "tug", which could return to LEO using aero-braking.
.

If this would be the way then the expendable Earth Departure Stage which has been spoken of would be a first step only to what I have been speaking about.



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Post    Posted on: Mon Oct 10, 2005 9:48 am
Take a look at this article from SpaceRef, its packed with technical information on NASA's proposed new vehicles. It contains lots of technical stuff I havent seen before and the slides from a presentation given by the National Academy of Science.

One interesting thing is that NASA is apparantly now saying that "they hope" to CEV will be reusable but this will be dependant upon the design process.


http://www.spaceref.com/news/viewnews.html?id=1069

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Post    Posted on: Mon Oct 10, 2005 2:59 pm
Wow Andy, what a GREAT link! :D
The plan looks really solid and achievable, improved over Apollo but not far fetched. One advance that stood out to me was the choice of propellants. No more hydrazine and nitrogen tetroxide. It will be LH2/LOX and methane/LOX. This greatly increases the capability of the system due to the higher isp. Apollo used all storable hypergolic propellant, which was the safe way to go but really limited the payload. It remains to be seen, however, if cryogenic, non-hypergolic fuels will be safe and reliable. Also interesting is the way all this is intended to be usable for Mars missions. Methane was chosen for the assent stage because of the possibility to manufacture it on Mars. I really like the idea of flying as much of the Mars hardware as possible to the Moon before going to Mars.


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Post    Posted on: Tue Oct 11, 2005 10:07 am
I am wondering what the reason is for having a descent stage and an ascent stage. It seems to me that this the real reason why the lander is expendable.

Is there a technical, technological or physical reason why it can't be avoided to have an a descent and an ascent stage instead of stage for both these purposes?



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Post    Posted on: Tue Oct 11, 2005 11:28 am
Using separate stages allows a smaller craft, its done for the same reason that rockets are multiple stages on earth. Having to lift a combined Ascent/Descent vehicle would result in more fuel being used during the ascent and hence a heavier vehicle. This vehicle would then require a heavier booster to launch from Earth.

One way round this would be to reduce the payload or crew to save weight but this is obviously less desirable because your return on the mission is reduced. There is some talk about the Descent stage being left behind to form part of a growing moon base so the approach NASA has chosen may not be a bad thing.

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Post    Posted on: Tue Oct 11, 2005 11:42 am
Yes, that I understand.

One of the reasons to wonder was that it seems that there will be significantly more missions or trips to the moon than in seventies of the last century. As the comparison between the expendable Soyuz and the reusable CXV in the Financial Barriers-section illustrates reusability and thus one stage for both descent and ascent could be advantegous then.

Having a descet stage and an ascent stage seperatly would mean that to make that lander reusable would require to carry a new descent stage for it each trip or mission if it would be made waiting in a lunar orbit - docked to a very small station for transit from CEV to lander perhaps. If the same stage would be used for descent as well as for ascent then this larger and heavier stage would need to be delivered only once and then could be used again and again for traffic between lunar surface and lunar orbit. No stages and no expendable landers would need to be carried from Earth - only propellant would have to be carried - and that also only as long as no lunar ISRU would provide it.

In that case the weight of the expendable lander would be saved which now has to be launched additional to each Earth Departure Stage need each mission newly.

If I would have numbers like those about the CXV I would look for the break-even-point in the Financial Barriers section but I don't have them and only can suppose that using the same stage for descent and ascent and the resuability would be the superior technology.



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Post    Posted on: Tue Oct 11, 2005 4:21 pm
If the landing vehicle were designed to use the same propellant and engine for decent and ascent, then I think the weight penalty of carrying the landing legs and larger but mostly empty fuel tanks back off the surface would be largely offset by the reduced overall weight due to no separate ascent engine or staging hardware. In short, I think performance is not the reason the lander is not fully reusable. My guess would be the operational hardware and procedures to refuel and refurbish it in space do not exist and would cost far more than the total budget of the project to develop. In time, the private sector may develop such a capability, but NASA’s mandate is to return to the Moon now at minimum cost, not to develop a fully reusable system. They already tried that with the Shuttle and failed miserably.


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Post    Posted on: Wed Oct 12, 2005 4:37 pm
I wonder if orion propulsions batwing could be applied to Falcon IX. The only problem is that it would reduce payload mass--if for no other reason than the fact that the two strap-ons must remain with the core for the fly-back mode to work--and it is the shedding of empty dead weight mass that makes strap-on separation a must to begin with.


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Post    Posted on: Thu Oct 13, 2005 6:45 am
I have been thinking more about what I said in my previous post here.

Given the concept NASA prefers it will be required to carry the propellant for the lander to the moon - so this can't be avoided for a while. What could be avoided is to carry a new lander each trip. It seems that I was considering a reusable lander that would carry the propellant for later ascent down the lunar surface with it - in the stage used as well for descent as for ascent.

This would mean that the lander requires a larger tank than needed for descent alone only or for ascent alone only - but this could be avoided too. The propellant for ascent could be delivered down to the lunar surface directly by an unmanned cargo vehicle. This cargo vehicle wouldn't require the safety equipment needed for the crew of manned vehicles. Then the tank of the reusable lander wouldn't have to be that large that it could carry the propellant for ascent too.

In lunar orbit only the propellant for descent would have to be fuled to the lander's tank.

It may be possible to make the unmanned cargo vehicle reusable, light-weight and foldable.



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