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Lesson 13 Archive Notes September 24, 2010

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Space Show Classroom Lesson 13:  Orbital Propellant Depots

 Thursday, Septembeer 23, 2010

 Archive Notes and Program Information

 The Space Show Classroom Lesson 13 can be downloaded or heard

at:

http://archived.thespaceshow.com/shows/1428-BWB-2010-09-23.mp3

Guests:  Classroom featuring Dr. David Livingston, Dr. John Jurist, Dr. Jim Logan and Dan Adamo, Dallas Bienhoff.  Topic:  Orbital Propellant Depot.  Welcome back to this Classroom program focusing on an intense and comprehensive 2 hour 25 minute two segment program.  Please note that as with all Classroom programs, your emails and comments are to be posted on The Classroom Blog at https://spaceshowclassroom.wordpress.com once this program is archived as the Lesson 13 Archived Program. I also want to point out that there were significant telephone line and audio issues on the lines with some of our expert panel members and I apologize in advance for less than perfect audio conditions.  This was a comprehensive and detailed discussion on the pros and cons of orbital propellant depots, the places to put them, economics, launches, constraints, regulations, and much more.  In our opening segment, Dallas started out by talking about the reference study, comments made by Dr. Mike Griffin as the NASA Administrator regarding the value of fuel in a depot to NASA and more.  Dan followed with some of the orbital constraints involved along with operational logistical issues.  At times this was a technical discussion but one that I believe everyone should hear and pay attention to because the discussion with Dallas and Dan along with the co-hosts was at a very high level and all of us learned a lot during this program.  Some of the issues we talked about during this segment included loitering on orbit for perhaps up to a week using the Orion and Altair.  You will hear why this is so and why the system was not capable of landing any where any time.  We talked about LEO depots, concerns and trajectory constraints.  Dan talked about Plain of Regression which is 7 degrees west and what this means for depot placement, Delta V, and ingress egress.  Dallas said that their study only looked at the Moon and never looked at other destinations.  The study he referenced was for back and forth to the Moon using L1.  Other topics addressed launch rates and the number of launches required to put a specific mass on the Moon using the depot as compared to using a heavy lift rocket.  The issue of divorcing a commercially operated depot from existing federal regulations was a hot topic in both segments with Dallas offering one view and Dan looking at the problem from a different perspective given his operational experience, specifically with the Eastern ranges.  The second segment started with our discussing docking with Dan pointing out why docking was risky and problem oriented, and Dallas talking about how we can and will use docking with the depots.  Dallas was also clear that the depot was not a replacement for heavy lift but an enhancement of capability for all launchers, including heavy lift. Later, when our guests were asked for their ideal programs, were we to be starting out with a fresh slate, no legacy anything, one would designs systems for specific environments and as Dallas said, you might not need heavy lift but that is not the world we live in today.  Launch and propellant economics and the business case for a depot came up during this segment.  Our co-hosts had many questions, we talked about cryogenic fuel boilff, power to the depot, and lots more issues.  Dallas outlined how its thought that the boiloff can be used to station keep the depot.  Other topics that were addressed were civil space traffic control, collision avoidance, Bigelow Aerospace as a customer, developing markets and customers, and the size needed for a heavy lift rocket.  Numerous other topics and issues were discussed by our experts and co-hosts during this program.  Remember to post your comments and questions on the blog. Please do not send tem to me but if you do, I will post them on the blog under your name.

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Comments»

1. John Hunt (in Atlanta) - September 24, 2010

The Dan Adamo/Dallas Bienhoff discussion (debate?) on issues relating to orbital propellant depots is loaded with valuable information that should be carefully analyzed by people interested in this important topic. The two experts are both highly knowledgeable about their topics. Dan’s specialty is flight dynamics and current real world operational issues. Dallas brings the expertise on the depot technology itself. This leads to divergent views on the type of depot that is preferred.

There is general agreement that depots main applicability in the next generation of spaceflight is in there applicability to lunar missions. The greatest disagreement is that Dallas favors orbit LEO depots and Dan prefers destination depots prepositioned on the Moon or other final mission objective. The leads Dan to see the requirement for 150 ton class HLVs for human lunar missions and the use of two of these large HLVs to accomplish a lunar mission. Dallas came prepared with studies that show the advantages depots can add to a single Ares V class mission utilizing LEO refueling prior to TLI. (I didn’t recall much discussion of this but Dallas did have truly alternative lunar mission architecture in item # 3 of his presentation material.)

In a sense I think the debate aspect was basically a draw. Since Dallas’s studies were conducted under restrictions to the architecture of the Constellation Program, I think this left his position weakened somewhat. This is because if we actually had an Ares V, Dan has a simpler approach from an operational view point. However, it is unlikely that we will have a very large HLV given the cancellation of the program of record. While we wait a final resolution from Congress, it seems unlikely that Ares V will be developed.

I have in connection with Dan’s last show (9/7/10) posted http://thespaceshowoutsidethebox.blogspot.com/2010/09/dan-adamo-on-propellant-depots-tuesday.html#comments in conception of an alternative that utilize a smaller launcher in the 50 ton class (should we call it a medium lift vehicle (MLV)?). My vehicle in addition incorporates as much reusability as prudent. My current concept is to make the first-stage reusable and the second-stage refuelable. There are some major options here including just recovering engine modules and not whole stages, etc. The point is that this second-stage refueled by a LEO depot has at greater TLI potential than the Ares V would have had. At the same time my proposed 50 ton class launch gives an economy of scale and there significant reusability (at least component-wise) to provide much lower cost per kilogram to LEO to establish and maintain depots than using EELVs and Falcon 9s

One other advantage that I see in the 50-ton class vehicle it that it is sized to be a general workhorse to LEO for a wide variety of missions. The large HLV would not only be intrinsically more expensive but would be produced in much lower quantities resulting in very high costs since it would be use only for very high end missions, i.e. Moon, large object to LEO, etc.

2. Joe - September 26, 2010

Comments only.

This by far is the most interesting classroom show I have ever heard! It was historical. It made me think. I also enjoyed the fueled discussions on the show. I couldn’t even begin to think of a good enough question to add to the discussion since I was so focused on the discussions that included masterful points and counter-points. Like me, I liked it when Dr Jim Logan mentioned he just wanted to listen. Dallas is a forward thinker with business profit in mind that is unstoppable. Dan is a true space operational and space pioneering master. He tried his darn best to keep Dallas from venturing too far outside of the historical operational reality box. Dallas and Dan made some admirable talking points. For listener feedback purposes, here is my summary of their talking points with a few extra ones not yet discussed:
1. NASA is interested in fuel depots and is interested in continuing funding to push the envelope of operational space missions to distant destinations.
2. The concept of fuel depots could be abandoned after a serious design oversight appears during a demonstration. Just saying it can’t work based on credentials is not going to stop the funding. The cat is already out of the bag, so to speak.
3. NASA and Boeing like the operational concept of unmanned autonomous docking for pre-positioning cargo (fuel and possibly supplies). It simply allows the crew to take much more equipment with them when they arrive at the depot to fuel up. It opens them up to more options than just collecting a few rocks and taking a few pictures. Who can argue with that? Boeing is already hard at work to include this autonomous rendezvous and docking technology in its Commercial Space Transport Vehicle that is competing with SpaceX and the Russians and even accommodate Bigelow Aerospace and Space Adventures customers.
4. Orbital Express Demonstration was so successful that the DARPA Program Manager was completely and utterly ecstatic. He shut down the program early since it met all program objectives beyond their expectations.
5. Docking problems, especially unmanned, can and do happen. When it eventually happens, it only jeopardizes the mission and does not constitute a safety hazard like what happened in Apollo 13. Ok, I’ll agree that it raises the stakes but it offers the crews more time to train for their mission. On an unmanned mission, the only loss is the cost of the launch which is offset by insurance. Who knows, if it happens during a manned mission, the crew could go EVA and fix it or fuel up manually, and become space heroes like they have done time and time again.
6. We are still politically restricted from launching nuclear transfer vehicles which is thinking too far outside of the box, so we are stuck with the logistical problems of storing cryogenic propellants in space.
7. Proposed solutions exist for 5 years already to address long duration cryogenic stages for exploration to passively limit hydrogen boil off to 1/10th of 1% a day which could someday be demonstrated on Flagship Technology Missions. Dallas even mentioned several conceptual ideas to lower that number even more. This begs funding to at least try them out. Proof is in the pudding.
8. The existence of fuel depots can be used by anyone who pays the price that makes the business case stick. That includes Bigelow Aerospace, a new space pioneering and cost conscious business entity.

Looking forward to the next classroom discussion. Outstanding, David! Thanks for all that you do.

3. Dallas Bienhoff - September 26, 2010

Depot Departure Opportunities Update.

Thought I’d provide some feedback about one of our discussion points – LEO Depot to EML1 or Moon departure opportunities. As you recall, I said 59 days between successive opportunities and Dan, correctly said, around 7-9. I did some checking and it appears the information I received was the result of an inverted positive/negative sign. I replicated the information I received and calculated the correct value, 213.3 hrs, or 8.9 days, between orbit alignments (every 180 degrees combined motion) at 400 km alt and 28.5° inclination orbit for the depot.

My error was to blindly accept the information received and not fully discuss or understand it before quoting it.

4. Terry Pickett - September 28, 2010

This was a great show! As always, I learned a lot.
I just think the business model will be a show-stopper. How much to build the depot, how much to maintain the depot, will you have enough consistent customers to make it profitable? I can’t imagine the cost to build one in LEO or L1, $30 billion plus?

5. Tom Hill - September 28, 2010

One point I heard Dan mention that I’d like to counter. He said that an awesome fuel to store in orbit would be water for nuclear-thermal rockets. While water is very easy to store, I’ve seen in multiple publications (one sample: http://www.neofuel.com/moonicerocket/, the site is non-mainstream, but it is based on an AIAA paper that’s cited in multiple other sites) that the Isp for a water/nuclear thermal rocket is less than 200 sec.

Of course, other options exist, electrolyzing the water into its components, then using the LH2, but that involves making cryogens in orbit.

Enjoying the discussion very much.

Tom Hill - September 28, 2010

Reading a bit more into the paper, they build a case saying that the decreased infrastructure mass in using water makes up for the lower performance. Their case was lunar ice, but I’d have to look to see how it translates to an orbiting depot.

Dallas Bienhoff - September 28, 2010

Water is easy to move and store and should seriously be considered, which is the approach preferred by Shackleton Energy Company, but it is best to use its constituents, oxygen and hydrogen as propellants or use sufficient energy in the water rocket to disassociate the water into hydrogen and oxygen before expelling it from the chamber to increase the rocket’s specific impulse (Isp), or efficiency.

As an example, let’s look at a round trip between LEO and the Moon’s surface, which requires approximately 30,000 ft/sec change in velocity. For simplicity, I’ll use 32,200 ft/sec. Also, for simplicity, let’s say the water rocket Isp is 200 and oxygen/hydrogen rocket Isp is 500.

Propellant mass for free-space rocket maneuvers can be found using the following equation and English units: Mp/Mbo = exp(dV/(gc*Isp))-1) where Mp is propellant mass, Mbo is the vehicle and payload mass at burn out (end of propellant), dV is the change in velocity, gc is 32.2 (a gravitational constant), and Isp is specific impulse. Mass is in pounds-mass, velocity is in ft/sec, specific impulse is pounds-force/(pounds-mass/sec), and gc is ft-lbm/lbf-sec2. Exp is the abbreviation for Exponential function e (2.718…) raised to a power, in this case dV/(gc*Isp).

Substituting the numbers above (32,200 ft/sec dV and 200 and 500 for Isp) gives a propellant mass 54.6 times the vehicle and payload mass for the water rocket and 2.7 times for the oxygen/hydrogen rocket. This is a single stage approach. Using multiple stages or refueling reduces that impact. If the total velocity change is made by a vehicle sized for 5 equal burns and is refueled between each burn, then water mass is 5 times the burn-out mass and oxygen/hydrogen is 2.5 times. Dividing the total velocity change into more than 5 equal units begins to increase the total propellant required.

Since the payload is typically larger than the stage pushing it and electrolysis and liquefaction units will likely produce many times their installation mass in usable propellants I find it hard to believe water, without dissociation, is a better system solution than oxygen/hydrogen from water.

John Hunt (in Atlanta) - September 28, 2010

Water is not the way to go on nuclear thermal except in the special case of using in situ resource utilization. The basic limitation on nuclear thermal is temperature that the core can sustain. The temperature of a gas is a measure of the mean energy per molecule. Water has a molecular mass of 18 versus hydrogen’s 2. Their ratio is 9. So at a given temperature the mean energy per particle is that same whether the propellant is steam or hydrogen. Since E = ½ m v^2 the velocity squared of the hydrogen molecules is the ratio of the mass or nine time that of steam. So taking the square root the velocity of the hydrogen is three time that of steam. And, specific impulse is proportional to velocity.

So stated simply, hydrogen gives you three times the specific impulse of water. At best with solid core nuclear thermal you are not going to out perform chemical fuels. This is why for Mars missions and such it is worth the trouble to go to liquid hydrogen as a propellant in a nuclear thermal system.

6. Dallas Bienhoff - October 11, 2010

John Hunt discovered a math error in slide 19 of my 100527_Cislunar_ISDC10_R1_NoVideo.pdf file. While the inert and propellant mass numbers were correct for each entry, the lander total and combined total for all systems were incorrect. I have sent an updated file to David Livingston so he can replace the current file.

Thank you, John.


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