Gravity Assist Competition

Or The Space Game, by ESA.

Minimize delta vee by moving the planets around (this changes the probe's arrival time at the planet). This shows my best solution so far, with some playing one evening, about 13 km/s

This is a nice javascript webpage where a probe is shot from Earth to Jupiter with gravity assists at Venus (twice), Earth and Mars. You try to achieve the lowest propulsive delta vee. You decide when the spacecraft arrives at each encounter and the program basically calculates the rest. It’s quite a nifty little piece of Javascript, the future of web applications is like this. It works fine with Chrome on Linux at least. Probably IE will have problems but who uses that anyway?

I’m ranked at #39 at 12.74 km/s… Far behind the gurus who get below 10 km/s readings! There are apparently some prizes for the top three, but I think people are in it for the fun of it.

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Humans Fast, Machines Slow

Rand Simberg talks about impedance matching. So I’d like to make a post of my comment there (I’ve always wondered why this obvious alternative gets mentioned so little…)

What to do when you arrive at Mars or Earth with your solar electric propelled vessel?

So, the problem with most low fuel demand velocity change schemes is that they only give slow accelerations. Low fuel high velocity change means solar or nuclear electric propulsion and aerocapture mainly.

High delta vee aerobraking is hard to do in one pass – it gets dangerous because of atmospheric variability and potentially other reasons.

Simple: detach a small capsule with the humans that goes directly to the surface (with only days of life support) and leave the untended craft to do multi-pass aerobraking. Hitting van Allen belts a few more times or taking a long time doesn’t matter that much with no humans onboard.

You could also potentially ultimately leave the long distance craft at some Lagrange point instead of LEO. (Cue some clever and complex maneuvers to save fuel – maneuvers that take long.)

Something similar could also be done when a long distance stack is assembled in LEO: send the humans there only after it’s through the belts. They can go with a smallish capsule again. Potentially at some Lagrange point, or in space without any fixed reference, just along the way. It could be dangerous though if the capsule doesn’t have much life support.

Many of these things have potential delta vee penalties as well as timing inflexibilities, but they could have enough other benefits that they should be considered.

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A Proposed US On-Orbit Propellant Transfer System

For the ISS. The shuttle would transfer unused hypergolics to the ISS propulsion module. ATV as well.

http://en.wikipedia.org/wiki/ISS_Propulsion_Module

It was canceled and instead Progress and ATV are used directly for most boosting. Nevertheless the technology could be useful in developing hypergolic propellant depots.

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Minus 2D Boom Rendezvous

I always had a different idea compared to the one Jon and Kirk posted, (Kirk Sorensen is now a contributor at Jon Goff’s place, I’m afraid having such top men in the same place might cause a awesomity criticality event). I assume this idea is probably found in some old NASA report from the sixties or seventies, like most things are.

Rendezvous is mostly a 4D problem: 3 space dimensions and time (some more if you take into account that proper attitude must be maintained as well, but that is assumed to be trivial). If you can take out two space dimensions, the problem should simplify greatly. This is possible with the following arrangement:

A boom at both the target and the vehicle, placed at right angles (and both at a right angle to the approaching vector). Basically, this should reduce positioning accuracy requirements hugely. The booms could be short barrels (even inflatable), or really long semi-rigid wires or composite girders or whatever. Depends on design aims.

When they contact, they will both slide until one boom is caught by a hook at the end of the other boom. Then one boom will slide through the hook until the hooks contact. From there on it’s a known geometry. You can reel in the boom, if it is flexible, or just slide it if it is rigid, and get both craft to a configuration you want, for either ordinary robot arm capture for berthing (as demonstrated by HTV, many station modules and Shuttle MPLM:s) or traditional docking (Soyuz/Progress/Shuttle/ATV).

This concept has some problems. For example whipping the target or the vehicle with an improper attitude / position boom. In the pictured boom configuration, approaches should have an offset always to one side. Alternatively one could have multiple booms. That way it wouldn’t matter on which side the rendezvous error would be. Also, the target could have a V shaped bow to avoid having the vehicle hitting dead center with a boom.

Another issue is if there is some kind of failure in the rendezvous, like too high velocity, the boom might rip off. That would result in a very dangerous object co-orbiting with the vehicles. This would be a very bad day for something like the ISS or a propellant depot.

One way to avoid this is to have the hooks have a mechanism to give way if the load gets too high. Another more outlandish is to have a weaker boom attachment in the vehicle. This would sever its boom and leave it hanging to the target in case of a problem.

This all was motivated to make unmanned rendezvous much easier to enable cheap propellant depot tankers. As all know, ATV and HTV are hugely expensive and high dry mass systems. Something like a Centaur or any basic “dumb” already existing restartable upper stage with just mostly a working attitude control system (including a star tracker) could be used instead, if some out of the box thinking is deployed. Most of the smarts should be in the target that is launched only once, but it can’t be the maneuvering party since it is very heavy. This system should get the best of both worlds.

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Dual Propellant Expander

Or what you are going to call it, an unrealized proposal from Aerojet around 1984. PDF Found on NTRS.

The idea was to have two turbopumps (like on SSME), but instead operate on the expander cycle. Two heat exchangers, two turbines, two pumps. One for each propellant.

 

Both propellants go through a heat exchanger and an expander driving a pump

 

This is a LOX-hydrogen engine. Also this means that since there is the same propellant on both sides of the axle, in the turbine and in the pump, no elaborate seals are needed. Original intent for these engines was for in-space reusable stuff, that needs to be operated many times and for a long time without maintenance. Size was in the RL10 class, about 70 kN. (RL10 has grown though.)

Simplicity and margin were claimed

Think for example if you let a fired turbopump sit in space for a long time. Will some fuel leak to the oxidizer side through the seals? This could avoid that. (You can use helium purges too though but then you’ve got one more fluids you need to tank.)

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Jeff Greason

The Man. On Space Review. [EDIT: About a month ago, but I only just read it.] This is just excellent. So many things I agree with, that go against the stupid myths of spaceflight and space policy. If you read one space policy interview this year, this should be it!

“NASA is an organization that is dominated by fixed costs. In business terms everything is in the overhead,” he said. The committee found, with some effort, that the fixed cost of NASA’s human spaceflight program is $6–7 billion a year. “The bottom line is that they can’t afford to keep the doors open with they money they’ve got, let alone do anything with it.”

…

However, he said, if you’re trying to minimize costs, it makes more sense to use a smaller launch vehicle that flies more frequently and has other users and applications. The key to making that work for exploration architectures that require large amounts of propellant—and hence have driven the planning for heavy-lift vehicles like the Ares 5—is the use of propellant depots and in-space propellant transfer. “If you use in-space propellant transfer, it’s no longer true that you have to have a really big piece,” he said.

…

He said that while he had his own opinions on the right selection of launch vehicles, he didn’t have any insights on what direction the White House and Congress would go. “It’s really up to policymakers whether we have a space program or a jobs program.”

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Delta IV Manrating

Skimming the document (thanks NSF, Florida Today). Cute how a launch without an upper stage at all in the heavy configuration works out for ISS (burn SM fuel for orbit):

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Reality and Future

Jeff Greason is a rational person who simply gets it. It is mind boggling how completely opposite from someone like Mike Griffin he is.

See Jeff’s presentation with the Augustine Panel.

Paraphrasing, “we could go to Mars with Ares V but we shouldn’t – cause we couldn’t stay anyway”. Exactly. That’s the problem with NASA. (or the major one)

I bet he will be ignored completely.

Also, I would like to work for that guy. Too bad because of ITAR I couldn’t work in the USA.

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My Letter to the Augustine Panel

In the previous post.

–

I’ve been very tired and felt completely unable to have any effect on my life or on any other things for the last five days or so. This doesn’t mean that I’ve felt lazy – rather that what ever reasonable I have ever done, it has had zero effect on the world.

There won’t be propellant depots. There won’t be thorium reactors. There will always be these huge problems in my personal relationship(s). Or interaction.

NASA will waste its money on some half built heavy lifter, if it ever gets so far. Launch costs won’t go down in my lifetime, and there won’t be any real RLV:s.

Coal burning will just accelerate and the globe will warm a lot by 2100. I won’t be here to see it. And even more after that.

It’s of course, as a single person, unreasonable to expect to change much in such things.

But what has most demotivated me always:

My hands are, have been and will be completely tied in interaction with certain human beings. I can not change the will or situation of some other person. I can’t really even effect it, if the other person doesn’t want to.

The loss of power seems incredible and overbearing at times.

The only thing that one can do with people is leave them and move on. That’s a very limited way of interaction. But that’s what it’s always been and seems to always be.

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Heavy Lift Unnecessary

There are a lot of implicit assumptions that heavy lifters of this or that throw weight must be used for future exploration beyond low Earth orbit.

These “needs” have never been logically derived from anything.

Yet space policy and exploration architectures must be based on rationality above all. There is no excuse whatsoever to do things on a whim. Hundreds of billions of dollars, and the future of humanity’s spacefaring are at stake.

There is no foreseeable need to launch over 25 tonne monolithic payloads to low Earth orbit in lunar exploration, and probably even that number could be seriously diminished with some more thorough planning. Orion, EDS, LSAM, all are below that weight, if they are refueled using a depot in space.

If the huge development and operational estimated costs for a heavy lifter rocket go away, then that money is freed for real exploration work. In-space hardware development, more launches, more missions and operations.

Flight rate is _the_ most important way of reducing launch costs, the single largest impediment for advancement of spacefaring, and the propellant depot enables a higher launch rate. Multi-launch scenarios with a propellant depot also enable competition, redundancy and flexibility, all very good things, ensuring safety, robustness and progress.

I repeat as a summary how

1) Solutions for space exploration, like any large endeavour, must be rationally justified. No baseless assumptions should remain.

2) The need of heavy lift is a baseless assumption. It can be one of the alternative ways of execution, but it can not be a starting point or an axiom.

3) The current architecture is heavily based on the implicit assumption of heavy lift. Hence a rational space exploration architecture would examine things from the ground up. It could end up with some radically different conclusions.

4) Propellant depots is one alternative way of executing space exploration beyond LEO, and it does not need heavy lift.

5) Propellant depots can, if executed correctly, increase launch rates many fold, and thus enable lower costs, progress, reliability, redundancy, robustness – all the things that the space shuttle promised but failed to do because it was a sole solution that could not sustain a high enough launch rate and was too costly.

6) NASA at the same time should keep on working with fundamental research, to enable continuous progress trends in space technology.

7) Space exploration should look as different from Apollo as possible – there should continuity and continuous improvement possibilities, robustness and progress. The architecture should be affordable as well.

8) New space technology, like cheaper launchers, should be demonstrated at a smaller, humble scale first. That way many things can be tried and progress is faster, for the same price and effort. One failure also will not be as critical.

9) There seem to be impediments for information flow inside NASA, and many professionally acknowledged things like propellant depots, EML2 rendezvous or space tethers are never even mentioned in NASA high level planning. This is not rational.

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