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Lesson Two Program, Advanced Depot Discussion, Tuesday, 4-5-11 April 6, 2011

Posted by drspaceshow in Uncategorized.

Lesson Two Program, Advanced Depot Discussion, Tuesday, 4-5-11


Guests:  Classroom:  Dan Adamo, Jon Goff, Dr. John Jurist, Dr. Jim Logan.  Topics:  This Classroom program was an advanced in-space propellant depot discussion. Please note that you are invited to comment, ask questions, and discuss the Space Show Classroom program/guest(s) on the Space Show Classroom blog, https://spaceshowclassroom.wordpress.com. Comments, questions, and any discussion must be relevant and applicable to Space Show Classroom programming.  We welcomed back our Classroom co-hosts Drs. Logan and Jurist and our two propellant depot experts, Jon Goff and Dan Adamo for a comprehensive graduate school level two hour discussion about propellant depots.  Also note that that as part of our upcoming Space Show webinar series, we did test video streaming during this program but as I said, we did not archive the video stream.  We will let you know when our next video streaming test will take place.  During our first segment, Dr. Logan set the tone with his opening statement when he said that resource pre-emplacement was essential if we were to go beyond LEO with chemical rockets.  Dan said the ISS was already a depot that transferred hypergolic bipropellant fuels.  This opened the door to cryogenic fuel transfer and a comprehensive discussion about boil off and the goal of reaching Zero-Boiloff Cryogenic Storage of the fuels in space.  Much was said about this, the energy needed to separate hydrogen and oxygen and why cryogenic storage was necessary in space.  We discussed some options were a depot to be located on the surface of the Moon but the issue of having sufficient power available for the separation is a significant one.  Launch windows, departure schedules, and depot locations were discussed.  We also talked about the idea of placing the depots in convenient places to attract multiple suppliers though this presents significant challenges with space traffic management problems.  In our second segment we started with a listener question about using NOFBX  and would it significantly help to reduce the complexity of a depot.  Jon Goff responded to this question.  Dr. Jurist brought up the issue of launch schedule reliability were it necessary to have between three to six flights including crew rendezvous happening within a specific time frame.  Both Dan and Jon referenced the Target NEO conference from February 2011, specifically the Chel Stromgren paper, “Getting to the Starting Line -Launch and Assembly Reliability for Deep Space Missions” (www.targetneo.org/Sessions/Session%203/TargetNEO-Session3-Stromgren.pdf).  During this segment, we discussed boil off rates and what this actually means regarding propellant losses and economic hits.  One of the recurring issues during our discussion focused on NASA Technology Readiness Levels (TRL). SpaceX heavy lift was discussed in the context of propellant depots as was heavy lift in general.  Bigelow hotels were also mentioned in the context of depots but there was also a discussion of why it might be too risky to put depots too close to human operated space hardware.  As our discussion was drawing to a close, our guests talked about the road forward. Each of our experts and our co-hosts provided short summary statements and as you will hear, each differed so don’t miss what each said.  We welcome your comments and questions so post them to our Classroom blog for this program.  If you want to email a specific guest, send your note to me and I will forward it to the person of your choice.


1. Jim Davis - April 6, 2011

This was an outstanding show. Both guests and all three hosts articulated their points quite well.

Jon Goff mentioned “gun launch” a few times during the show. Is there a particular scheme he had in mind?

2. Eric Collins - April 8, 2011

I tend to disagree with Jon’s statement regarding the utility of launching water, and then electrolyzing it into fuel in space. He seemed to be arguing that: a) it’s not very efficient (in terms of electrical energy in versus thermal energy out), and b) it takes to long. Well, if there are two things that we typically have in abundance in space, it’s time and energy.

There are several advantages to this approach. First of all, the tankers would share certain common aspects with resupply vehicles that would be delivering water to to manned stations anyway. The tanker would not need to incorporate any hardware for managing boil-off or cryogenic fluid transfer. Your mass fraction would also likely benefit from using only one tank instead of two. The tank mass would also be reduced due to water being more dense than LOX and LH2. Of course, all of the hardware for generating the energy, electrolyzing the water, and handling the cryogenic fluids would be kept in space as part of the depot, thus reducing the amount of redundant hardware that would otherwise need to be launched with each delivery.

As for the energy requirements for electrolyzing water, that situation may be improving as well. The following article (regarding the continuing development of Daniel Nocera’s work on electrolysis catalysts at MIT) was posted to Technology Review this morning:


3. Stephen Whistance-Smith - April 8, 2011

The reason I suggested turning the depot into the fuel tanks for an interplanetary craft is that over the life of the depot, and especially with the first few, there will be gradual improvements in design seen and made. One of the construction projects in the area of these early depots will be newer, better depots, and something will then need to be done with the old tanks.

Unless there is a complete change in the type of thruster systems used, incorporating an old depot into the framework for a deep space planetary exploration craft is likely the best use of available resources, so you are not really losing your depot as re-purposing the components of something that would otherwise be discarded anyway, hence the better bang for the buck comment.

Point of note, since fuel depot locations are likely to become hubs of activity for future endeavors their orbital positions need to be chosen with care. Although the first few will likely go up as proof of concept ventures, unless the investors are then willing to abandon those sites, perhaps boosting the components to a new and better position (were it cost effective to do so), re-purposing would seem to be the best option for clearing the space.

J M Jurist - April 8, 2011

Valid arguments. What are the relative mass tradeoffs for the depot itself? Thank you for your interesting comment. JMJ

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