Comments on: Square One: “Unaffordable” Lunar Return

By: Robert Clark

Robert Clark — Wed, 04 Sep 2013 07:04:13 +0000

Thanks for that. What’s key is that it only had to be 1/3rd the size of the Altair, making possible a much smaller, and cheaper, mission than Constellation.

Bob Clark

By: Robert Clark

Robert Clark — Thu, 29 Aug 2013 00:34:28 +0000

Paul, I looked up the field tests conducted on Earth of the RESOLVE ISRU testing program. They didn’t take place in arctic conditions and from what I was able to determine they did not do the extensive tests of having robotic excavators and robotic conversion of ice into hydrolox propellant under human direction with 3 second time delay.
Such tests would go a long way to proving the viability of this taking place on the Moon.

Bob Clark

By: Robert Clark

Robert Clark — Thu, 29 Aug 2013 00:24:29 +0000

On SpacePolitics.com now is being discussed an interview by Lori Garver where she said the medical community would not sign off on an asteroid mission lasting hundreds of days. Then since a Mars mission under current plans would be even longer that would mean they would also not sign off on a Mars mission even if we could afford it.
This is further support for the idea of getting the propellant from the Moon. You could have virtually unlimited propellant that could allow the trip to be done in weeks rather than months.
If this really is the view of NASA that their current Mars missions actually can not be implemented for medical reasons then that should be openly discussed so that realistic alternatives can be developed.

Bob Clark

By: Marcel F. Williams

Marcel F. Williams — Tue, 27 Aug 2013 08:24:55 +0000

Of course, the use of a lunar orbiting fuel depot could be avoided by simply being able to launch two SLS vehicles within a few days of each other.

But if the SLS launch rate was limited to just one launch every 6 months then you’d have up to 6 months to convert water into hydrogen and oxygen at a fuel depot placed in lunar orbit — not just a few days.

Or you could simply launch the depot with the fuel already stored, using cryocoolers to re-liquify the ullage gasses.

But excess oxygen produced at an orbital depot could also be utilized if the arriving lunar vehicle was already partially fueled with liquid hydrogen.

But once fuel is being manufactured on the lunar surface, the orbital fuel depot would no longer be needed and could probably be moved to a Lagrange point to help fuel future Mars missions.

Marcel F. Williams

By: Warren Platts

Warren Platts — Tue, 27 Aug 2013 01:50:00 +0000

Passively cooled cryodepots don’t require energy either, nor do they require energy for cracking and liquefaction. ISS has a 1kW system that evidently cracks about 6 kg of H2O/day. A system that could produce 10’s of tonnes of LH2/LO2 on a just-in-time basis would be measured in megawatts. Also, you’re forgetting that the optimal mass ratio for LO2:LH2 is 5:1–not the stoichiometric 8:1 of water. It doesn’t make sense unless one’s goal is unaffordability itself–something to invent in order to discredit the very idea of propellant depots IOW….

By: Robert Clark

Robert Clark — Tue, 27 Aug 2013 01:21:06 +0000

Old Atlas, did you work on the original Atlas rockets? I was struck by the remarkably high mass ratios of these rockets using the “balloon” tank design. If you combine those highly weight optimized stages with modern high efficiency engines then you can get high payload to orbit with surprisingly small rockets.
Do you know if any of the old Atlas rockets are still extant?

Bob Clark

By: Joe

Joe — Mon, 26 Aug 2013 15:23:58 +0000

The problem is the infrastructure that existed until the Shuttle Shut Down was sufficient to support up to 8 SDHLV launches per year.

If “the powers that be” have purchased new equipment that has only a quarter of that capability, they did not do it to save money. They did it to intentionally reduce capability.

This is the same issue as with the launch pads, they do not need to build a new one. They already have 2 and are trying to sell one off.

In an effort to save us both from the risk of meta-carpal tunnel syndrome, I will close by saying that the same basic principle applies to all the other components/subcomponents of a SDHLV. The infrastructure was there to support an 8 flights per year flight rate. If that has now been degraded to no more than 2 flights per year, that degradation was not caused by affordability. It was done for political reasons.

By: Robert Clark

Robert Clark — Mon, 26 Aug 2013 09:39:49 +0000

I like the ULA proposal that uses the Centaur for a horizontal lander. This would give a lander less than half the size of the Altair. Note also since you would not be developing a whole new stage from scratch the development cost would be much reduced.
In regards to the objection to using a “ballon” tank type stage for the lander, note that it doesn’t even have to be the Centaur. Both the Delta III and Delta IV rockets also have hydrolox upper stages of comparable size to the Centaur, but they do not use ballon tanks. These would also provide currently existing stages that could be used for a lander.
Either of these would result in a mission size less than half that of Constellation. Note in this latest NASA study by using two 105 mT- capable SLS launches for a total of 210 metric tons capacity to LEO, this is a mission size actually larger than Constellation. In point of fact by using the hydrolox landers half-size to the Altair, it can be done just using a single launch of the 70 mT interim SLS to launch in 2017.
An argument made in defense of the Altair is that this large lander is needed to deliver large amounts of cargo to the lunar surface, ca. 15 mT. But I was startled to find that a Centaur stage can even deliver more! If you’re making a pure cargo flight without crew capsule just to be one way to the lunar surface, then the Centaur can deliver more than 20 mT to the lunar surface.
This is under the architecture to be comparable to how the Altair was to be used of the lander providing the burns both to insert into low lunar orbit and to perform the landing. But if you only required the lander just to do the landing itself, than it can be more than 30 mT payload for the Centaur. The other choices for a half-sized lander derived from the Delta rocket second stages not being as weight optimized would not be as high, but they would still be higher than the Altair.

Bob Clark

By: Marcel F. Williams

Marcel F. Williams — Sun, 25 Aug 2013 22:50:22 +0000

Storing water for long periods of time in space (days, weeks, months, or years, centuries) shouldn’t require any energy at all.

And using solar energy to convert water into oxygen and hydrogen is done at the ISS all the time. That’s how they produce their air.

Liquifying hydrogen and oxygen is energy intensive. Fortunately, there’s no shortage of solar energy in cis-lunar space.

And NASA has already invented crycoolers that can store liquid hydrogen for several months or years.

Marcel F. Williams

By: oldAtlas_Eguy

oldAtlas_Eguy — Sun, 25 Aug 2013 20:31:22 +0000

The manufacturing limitation showed up in an article about the new tank welding machine talking about how many tanks per year it could manufacture. If they buy another machine and allocate more manpower and space they could increase this to 4 per year easily. So you are correct that this limit is soft but so is pad limitations because you can always build an addition pad if you need to launch more often as well. It just requires capital investment expenditures (government development funds) instead of operations expenditures (operations funds).