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Drs. Jim Logan and John Jurist, Sunday, 7-13-14 July 14, 2014

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Drs. Jim Logan and John Jurist, Sunday, 7-13-14


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Guests:  Dr. John Jurist, Dr. Jim Logan.  Topics:  EVAs, spacesuits, Moon, Mars, radiation, Aquarius HSF launch vehicle Space Enterprise Institute.  Please direct all comments & questions regarding Space Show programs/guest(s) to the Space Show blog, https://thespaceshow.wordpress.com.  Comments & questions should be relevant to the specific Space Show program. Written Transcripts of Space Show programs are a violation of our copyright and are not permitted without prior written consent, even if for your own use. We do not permit the commercial use of Space Show programs or any part thereof, nor do we permit editing, YouTube clips, or clips placed on other private channels & websites. Space Show programs can be quoted, but the quote must be cited or referenced using the proper citation format. Contact The Space Show for further information. In addition, please remember that your Amazon purchases can help support The Space Show/OGLF. See http://www.onegiantleapfoundation.org/amazon.htm.  For those listening to archives using live365.com &rating the programs, please email me as to why you assign a specific rating to the show. This will help me bring better programming to the audience.

We welcomed both Dr. John Jurist and Dr. Jim Logan back to the show to discuss spacewalks (EVAs), spacesuits, human missions to the Moon and Mars, to the Martian Moon Deimos, the newly created Space Enterprise Institute, & the new Aquarius Reusable Human Spaceflight water based launch vehicle.  During the first segment of our 2 hour 5 minute program, our guests started talking about EVAs.  Early in the discussion, Dr. Logan provided us with important & interesting statistics regarding EVAs, then we discussed the challenges with them and spacesuits.  We talked at length about the difference in EVAs and spacesuits for the Moon, LEO, asteroids, & Mars.  We also talked economics for spacesuits given the need for a specific spacesuit depending on the destination/mission.  We talked about new designs for one size fits all & for mitigating dust problems.  Jim talked about the medical complications regarding both lunar and Martian dust.  Our guests then suggested that EVAs will likely be phased out for robotic missions.  Doug asked several questions about this via email.  Also, Jim suggested that EVAs will evolve to the concept of Forward Deployed Humans in the Loop for Telerobotic Operations.  This concept was discussed several times throughout our program.

In our second segment, Jim started with an announcement about the Space Enterprise Institute (SEI).  When it goes live in the next week or so, I will announce it on the show so you can follow it  He explained SEI, its purpose & goals.  He then talked about the concept that both Jim and Dan Adamo have developed over the past few years, Aquarius which is a reusable water-based interplanetary HSF transport.  As soon as the SEI website is online, listeners will be able to download their peer reviewed paper for free.  During this segment, Jim talked about Aquarius, John added in some details, we talked about the need for nuclear electric propulsion and why, plus the role of water with this launcher.  Both our guests explained the advantages of Deimos for the early missions, plus the return shielding and reusability as the return goes to a lunar orbit using existing water.  Radiation shielding was talked about, including the needed water and needed Radiation Protection (RP) levels.  John pointed out one advantage of Aquarius was the use of an open loop life support system.  John in Ft. Worth called about the temperatures that Jim said were needed.  Jim explained the need for 3,000 degrees C.  Both guests offered closing comments about EVAs & the direction we might be heading toward the forward deployed humans concept.  Both guests said the telerobotic concepts discussed would reduce risks, timelines, & overall mission costs.

Post your comments/questions on TSS blog.  You can reach our two guests through me.


1. The Space Show - July 17, 2014

Please note that this post is on behalf of Dr. Jim Logan. In addition, as noted on The Space Show, the SEI website is now active. Visit http://www.spaceenterpriseinstitute.org.

“Thank you for your thoughtful and detailed comment!

The reference in the Aquarius paper for Assumption A05, Section II (Interplanetary Transit Assumptions), bottom of page 4, is:

Drake, B.G. (ed.), Human Exploration of Mars Design Reference Architecture 5.0, NASA/SP-2009-566, 2009, Section 4.3, In-Space Transportation: Nuclear Thermal Rocket Reference, page 25. The document can be downloaded at http://www.nasa.gov/exploration/library/esmd_documents.html

At P=1atm water begins to dissociate into atoms around 2600 C. Atom production but becomes more prominent as core/exhaust temps rise. At 3000 C, fully 35% of water vapor dissociates. At core temps greater than 3500 C mole fractions hydrogen and oxygen atoms dominate the reaction. By 3800 C, the mole fraction of water vapor is only 0.1 (out of a total of 1). So the process doesn’t go from 0% to 100% at precisely 3000 C.

I don’t pretend to be a rocket scientist (I’m a space doc). I have to depend on other more mathematically gifted experts. You may very well be correct that at exactly 3000 C, Isp is ‘well short’ of 900 s. BUT the point is chemical rockets are pretty much optimized at an Isp of around 460 and we’re going to have to do considerably better than that – like by a factor of 2! Chemical rockets can’t and won’t get much better even if zillions of dollars are thrown at them.

Human interplanetary transits will require high Isp (to minimize mass and volume) AND high thrust (for more rapid transit and abort capability). NTP is the only demonstrated technology I am aware of that can deliver the goods. If you know of another, please let me know. Several technologies have very high Isp but they have very low thrust and therefore aren’t viable options for long-duration human deep space transits.”

Jim Davis - July 17, 2014

Thanks for the reply, Dr. Logan.

A few points:

1. Note that the NTR in the reference provided operates on LH2 and at 1000 psia chamber pressure. The amount of dissociation at 3000 °C and 1000 psia will not be much. Here are the equilibrium mole fractions at these conditions:

H2O 8.3721E-01
H 6.5183E-04
H2 8.4621E-03
O 4.5481E-03
O2 4.2444E-02
OH 5.3477E-02
HO2 2.2027E-04
H2O2 2.8216E-05

The molecular weight works out to be 16.9 g/mol.

2. Note that your chamber temperature, 3000 °C, is just about the same as the chamber temperature in a conventional LO2/LH2 rocket engine. Since the working fluid in both cases is composed of H and O atoms (with a greater proportion of H in the case of the conventional rocket) you can hardly expect to exceed chemical Isps at these conditions.

3. Since your proposal relies heavily on a NTR that uses water as a working fluid and delivers a specific impulse of 900 s I *strongly* encourage you to really nail this down, if possible. As Dr. Logan said on the show “Without numbers, all you have is ideology.”

Thanks again and good luck with SEI.

2. Jim Davis - July 16, 2014

I have downloaded the Aquarius paper. I haven’t read it in its entirety but have serious reservations about whether the nuclear engine can deliver the specific impulse claimed. Would it be possible for the authors to provide a reference to a detailed thermodynamic calculation that predicts 900s at 3000 °C with H2O as the propellant? At that temperature water doesn’t completely dissociate until pressures are very low (sub atmospheric) and even under very favorable expansion conditions the specific impulse is still well short of 900s.

This is the type of calculation I mean:

PRESSURE (PSIA) 150.000 87.155 .062
EPSILON .000 1.000 199.999
ISP .000 139.654 444.329
ISP (VACUUM) .000 264.478 461.961
TEMPERATURE(K) 3337.105 3194.780 1629.175
MOLECULAR WEIGHT 15.615 15.845 17.979
MOLES GAS/100G 6.404 6.311 5.562
CF .000 .650 2.068
PEAE/M (SECONDS) .000 124.824 17.632
GAMMA 1.203 1.201 1.208
HEAT CAP (CAL) 75.431 74.918 64.137
ENTROPY (CAL) 398.891 398.889 398.891
ENTHALPY (KCAL) -20.565 -42.971 -247.367
DENSITY (G/CC) 5.82033E-04 3.58450E-04 5.63313E-07


H .28760 .24794 .00038
H2 .82862 .76074 .01981
HO .63610 .56050 .00458
HO2 .00094 .00065 .00000
H2O 4.25980 4.38547 5.52855
H2O2 .00007 .00005 .00000
O .12908 .10820 .00007
O2 .26190 .24762 .00881

Thanks and I enjoyed the show very much.

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