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Gemini 060615 released!
25068 Posts in 2094 Topics by 2266 Members
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1  Meadville Space Center / NEW MEMBER REGISTRATION / Re: NEW MEMBER REGISTRATION on: January 25, 2011, 09:00:01 PM
Snag.  I kinda figured that because the After Columbia Project forums currently get no other kind of activity.  I had to do this to the Egroup (now Yahoo Group) years ago.  Silly bots, ruin it for everyone, despite all those warnings from the sci-fi authors  Sigh
2  General Projects / Sprint / Re: Sprint Ferry Overview on: January 05, 2011, 07:01:40 PM
I discovered that the Fregat upper stage was far too heavy to ascend on the Delta II, at least in any low energy mission.  It's been a few years, and at the time I made the original post, Atlas V 402 was the leading vehicle.  I prefer a booster without ascent SRMs because you can't safely shut them down.  Today, I'd say that Falcon 9 is the booster of choice.  Also, the SpaceX Dragon is so close in characteristics to the Sprint, that it really doesn't stand much of a chance in the current market.

I have given some fairly recent thought to Sprint, including the story of its harrowing first flight in the world of Featherwing Love:

http://www.bookrix.com/_title-en-terry-wilson-breakwire
3  Project Apollo - NASSP / Project Apollo - NASSP News & Discussion / Re: IMFD on: April 23, 2007, 08:27:35 PM
The ONLY way to fly between planets.
4  Project Apollo - NASSP / Project Apollo - NASSP News & Discussion / Re: The eagle has landed on: April 23, 2007, 08:24:45 PM
One problem is that you have to do the stuff in the right order.  In reality, they combine all these maneuvers, however in Orbiter, there is no practical way to do that (except possibly using IMFD and targeting your command module like a planet, but I haven't tried that.)

1. Ascent:  Do your best to launch into the plane of the command module's orbit.  This is probably not possible if you've been sitting on the moon for a couple of days, but you should still be able to get fairly close by launching into a direction parallel and in the same heading to the command module's trace (which should still be pretty close to your landing site.)  Ascend into an orbit no more than 100km circular, you need to preserve your propellant.

2. Align planes (Shift-A): This instrument shows the relative inclination and the crossing nodes.  It is best to have it alongside your OrbitMFD (Shift-O) during maneuvers.  The new Orbit HUD works really nicely at finding your normal+ and normal- points (usually called "normal" and "anti-normal")  If you aim ahead "heads up and wings level" into the direction of flight, normal+ will be on your left, and normal- will be on your right.  To help visualize which way you need to turn, use the Map MFD (Shift-M).  Plane change maneuvers are only practical shortly before you reach a crossing node.  I learned very much the hard way that you _must_MUST_ start the maneuver before you reach the node.  Once past the node you are moving away from the target plane, which makes it very hard to "turn into" it, which is what this maneuver is supposed to do.

For Apollo, I recommend doing it with the Command Module.  I haven't actually flown NASSP, but from reading the history books, I know that the Command Module did these maneuvers.  What I wouldn't recommend for your first attempt is doing the plane alignment maneuver before lifting off in the LM...which is what they did historically.  The first three landing missions didn't need to do this...the third one especially, 'cus it didn't actually land.

3. Phasing, known in Orbiter as Synchronize, (Shift-Y): This is often where I get screwed, especially if I have non-spherical gravity turned on.  If ascent and plane alignment went well, you'll probably have a situation where your LM orbit is well below the CM and you have "No intersect" on the Synch MFD.  Gently raise the LM's orbit until the Synch MFD lights up.  At this point you should have a rendezvous longitude (a dotted line sticking out from the center of the Moon in the MFD, you should always have the two solid lines tracking the craft.)  Finally, you should have two columns of numbers.  One's something like "Sh-ToR" and the other is something like "Tg-ToR".  The first is the craft you're in (the LM), the second is the rendezvous target (the CM).  What you want to do is get one pair of these numbers within one second of each other (the MFD will highlight the closest pair; if it is the bottom pair, accellerate time and wait for it to move up to being the second last pair.  When it's at the bottom, it means your rendezvous opportunity a long way away.)  If Sh is getting to a spot a few seconds early, raise the orbit to slow it down.  If Sh is getting there late, lower the orbit to speed it up.  Make sure you are doing these raise/lower maneuvers carefully aligned to prograde or retrograde so you don't screw up your orbital planes (established in Step 2).  If you are lowering your orbit and going to "no intercept", raise it again, even though you're getting there early, and then wait for the apoapsis to try again.  This should keep the intersect.  Also be aware that the intercept moves when you maneuver.  Watch for this as sometimes it produces really counterintuitive behaviour.  I got pretty confused on my first couple tries.

4. Wait for the Synch intercept.  You should be very close to the CM when the time arrives.  The maneuver to match speeds with the CM is called Terminal Intercept (at least in modern parlance.)  You should be within 2000m.  Use the Dock HUD, set up your comm channels, and the Dock HUD will put up a pip for you to aim at.  Simply aim at the pip, thrust until it reaches less than 1m/s and there you have it.

If you are too far away for a docking approach or visual contact, the first thing you need to do is make sure you aren't going to crash.  Once I did such a maneuver while 20km from the ISS (suicidally distant) and accidentally deorbited myself.  If this sort of thing happens, you have to go back to step 2, probably wasting a huge amount of fuel and time.

5. Thrust towards the target, close at about 10m/s.  Your "reverse" pip should be on the target.  If it is sliding off the target and it is hard to keep it on target using infrequent pulses of your RCS, or the velocity value is changing too quickly, then you are too far away.  Once you arrive within about 100m, switch to the Orbit HUD, and then circle the around the CM laterally (i.e. relative to the surface of the Moon) until the CM is directly prograde or retrograde to your orbit.  Make sure to halt your lateral motion.  This keeps you from entering a scissor-like, really, really annoying orbital oscillation called a "wifferdill" (by the Gemini crew who first experienced it.)  The wifferdill is caused by being close to, but slightly out of plane with you're rendezvous target.  The Alignment MFD (Shift-A) can help make sure you're not in one.  Once in place, switch back to the Dock HUD and cancel out any relative velocity.

6. You are now stationkeeping.  Dock at your liesure in much the same way as the initial approach in Step 5.  The Dock MFD instrument (Shift-D) is really good at keeping your ports aligned, once you've figured out how to use it (instructions are in the Orbiter Manual, but you really haven't done it until you've done it.)

NASSP might have some more specifics.
5  General Projects / Mars Challenger / Re: Mars Challenger Overview on: April 23, 2007, 07:38:39 PM
Thanks, Mars Challenger is complete and was sent in near the end of February.

I was working on Symtex, but put that on hold for something I feel is more important to get done first: the MarsDrive Baseline Mission.  There isn't (officially at least) a contest to do this, and I'm hoping rather to spur a team effort to develop a plan to send humans to Mars which is both more feasible and higher fidelity than any plan that has flown before (on paper or in Orbiter of course.)

The thread on the MarsDrive Mission is here:
http://marsdrive.com/phpBB2/viewtopic.php?t=312
6  General Projects / Mars Challenger / Re: Mars Challenger Overview on: February 26, 2007, 01:22:00 PM
Mars Challenger is online at http://aftercolumbia.tripod.com (remember to turn on your pop-up blocker!!)

Abstract: http://aftercolumbia.tripod.com/id14.html
Full Report (1.56MB): http://aftercolumbia.tripod.com
7  General Projects / Mars Challenger / Re: Generic Mars Ascent Information on: February 26, 2007, 12:55:30 PM
I only discovered it a couple days ago and was too busy with the report to post it.  Check out the handy porkchop plotter at http://www.astrojava.com/TrajectoryPlanner.html.  Plot your own porkchop plots with this handy tool.  There are other handy tools too, check out www.astrojava.com.
8  Meadville Space Center / Site News / Re: Hacked on: November 05, 2006, 02:53:18 PM
Smilies don't work?  Dang Bangs Head Duh! Gloomy No Sigh Sorry Stop Worried Yuck! Zip Lip What? Shocked Sad Crying or Very sad Undecided Embarassed
9  Meadville Space Center / Site News / Re: Apollo forum bug? on: November 05, 2006, 02:50:29 PM
I can still post somewhere, I guess.  I've had the same plague.  I could post only in After Columbia Project.  Perhaps there is someone who thinks that's the way it should be  Excited!
10  General Projects / Mars Challenger / Re: Mars Challenger Overview on: November 02, 2006, 08:21:28 PM
New tweaked abstract:

Mars Challenger: Two Landers, One Mission: Mars Sample Return
 
Terry Wilson
After Columbia Project
 
Abstract
 
Mars Challenger is a sample return mission concept using In-Situ Resource Utilization (ISRU); After Columbia Project's entry into the MarsDrive Contest.  ISRU was originally conceived by Dr. Robert Zubrin in 1989 for a piloted mission plan entitled Mars Direct by putting together three industrial chemical reactions in a relationship capable of producing oxymethane propellants using seed hydrogen brought from Earth with locally acquired carbon dioxide.  Mars Challenger uses two elements, the Judith Booster and Christa Rover, which are launched together on a common launch vehicle and cruise stage, but are landed separately on Mars near each other in the Marte Vallis region, where there are recent Amazonian era water channels and the small possibility of discovering current life.
 
The dominant element is the Judith Booster and its accompanying fuel plant capable of compressing locally acquired carbon dioxide for use in a Sabatier propellant reactor.  Water from this reaction is then electrolysed to recover the hydrogen for recycling, and the oxygen for the propellant oxidizer.  Mars Challenger eliminates the least critical and most difficult of the three reactions used by Mars Direct.  This increases the liquid hydrogen seed requirement to exceed the total volume of the propellants which will be used for the return ascent.  The extra hydrogen is required to provide for generation of additional water from the Sabatier reactor, which is then electrolysed for the oxygen captured from the Martian air by the Sabatier reactor.  Excess methane, containing the hydrogen premium, is vented.  This applicability of this technique is probably unique to the scale of a sample return mission and inefficient for piloted mission designs.
 
The Christa Rover, which is landed up to several kilometres away from Judith uses its suite of scientific instruments on route to the booster to examine sites and select samples.
 
For reasons of cost and politics, both craft are electrically powered by solar arrays, with a small amount of nuclear radioisotope material in heating units, Christa's scientific spectrometers, and the control sample sterilizers for its laboratory style experiments.
 
Proven technologies and off the shelf or derived hardware will be used throughout to keep development and qualification costs to a minimum, however several technologies must be converted from terrestrial equivalents into flight hardware, and the protecting the mission's biological integrity is expensive in any case.  For example, the development of hydrogen compatible ascent tanks must be done from scratch.  The author is convinced that this mission can be accomplished for $800 million on a six year schedule.
11  Orbiter Mars Direct / Development / DIRECT Launcher: Should we switch to it? on: October 29, 2006, 03:45:27 PM
Ross Tierney and Antonio Maia ("simcosmos") have brought Baker/Zubrin Ares up to date and called it the DIRECT.  This booster is characterized by:

- Has 2 RS-68 engines under the core; standard version plans to have regenerative engines
- The homework isn't complete, but it plans to use the existing ET hydrogen tank, interstage, and aft LOX dome, with a minor redesign of the ET hydrogen aft dome to accommodate the thrust structure and manifold interfaces.  The new LOX tank will be smaller (RS-68 has a lower mixture ratio) and an ellipsoidal forward bulkhead similar to the LOX tank's aft bulkhead will be used.  BZ Ares is very similar, but has a LOX tank of the same volume as on the existing ET.
- It uses standard 4 segment RSRM boosters, just like the Shuttle already does.
- The CLV variant doesn't have an upper stage, but the CaLV variant, with the same lower stages, uses an EDS upper stage almost identical to that of the BZ Ares with my proposed mods (common bulkhead tank.)

Performance of the standard CLV is 70,900kg to LEO.

TASS2 analysis of the BZ Ares has revealed that its performance does not significantly exceed this.  TASS2 implements the following, most of which were not implemented in our BZ Ares model and the version of Orbiter it was originally drawn up for (IIRC it was either 020217 or 030303.)

- Underexpansion of nozzle gasses at low altitude
- Atmospheric drag
- 103.5sec full blast SRB (i.e. no thrust bucket; I believe our ZB Ares runs full thrust for 124sec, which would have the side effect of increasing Isp well beyond that attainable for solid propulsion.)
- Other differences are slightly conservative, and become liberal (and outrageously so) only once the booster reaches circular velocity.

At ERV payload, TASS2 estimates that BZ Ares is about 1200m/s slower than it is in Orbiter at 1/2 staging.

Send me an email to aftercolumbia at gmail dot com if you would like a copy of TASS2-ZBAres.xls; it is too big to put in the Yahoo Group file section.  If you can't take a big attachment, tell me, and I'll trim it down so it can be restored using fill commands.  I'll be converting it to DIRECT shortly in terms of my contribution to OMDP, but it'll be a while before I can get back to OMDP...other projects call.
12  Project Gemini / Discussion & Help / Re: I think I sould say something here on: October 25, 2006, 07:27:34 PM
My earliest space memory was looking forward to Voyager 2's flyby of Uranus.  I wasn't quite as tiny as that, however.
13  Project Gemini / Discussion & Help / Re: entering the atomspthere on: October 25, 2006, 07:25:26 PM
Last time I did it in a Gemini was a long time ago, but I know both OAMS and deorbit module work.  One thing it took me a while to figure out is that the lift comes out of your... Zip Lip...better not say that.  Suffice it to say, enter heads down, aft end first for bets results.

I did a more detailed answer to the general problem of entering lifting vehicles at http://aftercolumbia.tripod.com/entrytutorial based upon the Delta Glider.  Gemini starts flying like a rock at about 4500m/s, past that point its pretty much waiting for the parachutes.
14  General Projects / The After Columbia Project / Re: A brief introduction to ISRU for Mars on: October 15, 2006, 10:17:32 AM
In my second look at this article, I realize that I made it sound like storing hydrogen in space was easy.  Herschel uses a helium tank similar in size to Judith's entire supply.  It is too heavy to be used in the ascent application, and the real problem with long term liquid hydrogen storage is not the cold temperature, but material compatibility.  A lot of metals absorb hydrogen and become brittle, especially titanium.  This is the problem that demands an all new tank.
15  General Projects / The After Columbia Project / A brief introduction to ISRU for Mars on: October 14, 2006, 11:38:01 PM
 Shocked

During the development of Mars Challenger's design, I learned a lot about the challenges of In-Situ Resource Utilization, especially the partial ISRU plans that dominate piloted Mars mission designs, such as Mars For Less, Mars Direct, or the particularly infamous NASA Design Reference Mission (the second most expensive way to get to Mars after the Space Exploration Initiative.)  Basic Sabatier/Electrolysis ISRU uses the following two chemical reactions:

(1) Sabatier Reaction (Also known as Reverse Water-Gas Shift)
4H2 + CO2 -> CH4 + 2H2O

(2) Hydrolysis (a.k.a. Water Electrolysis)
2H20 -> 2H2 + O2

The first one is super simple, slightly exothermic catalyst bed type reaction.  The reactor resembles a car's catalytic converter and the first one used for ISRU related testing was designed and assembled by Dr. Robert Zubrin in a matter of hours in 1989 (with a couple months of waiting for ordered parts in between.)

Hydrolysis, primarily used for making high purity hydrogen, is much more "expensive" and difficult.  There are a lot more design choices, including type of electrolyte, cell voltages, etc.  The reaction is highly endothermic, but as we shall soon see, the electrical requirements of hydrolysis for Mars ISRU are not such a big deal after all...

Physical Processes:

It wasn't a surprise when I found out that the ISRU production concept is dominated by its physical processes.  In Mars Challenger, I'm trying, very literally, to pull over two tonnes of finished cryogenic propellant out of thin air.  Rabbits and top hats notwithstanding, the dominant process having to do with thin air is compression.

On Mars:

You actually need two compressors, one for the Sabatier and one for the fridge.  The best fit of Earthly equipment to the task of liquifying the propellant is Cryomech (www.cryomech.com) Gifford-McMahon helium cryocoolers (i.e. the AP300/CP970 system.)  As far as compressing Mars air...well...you need a compression ratio of about 1200.  The equivalent on Earth would generate some 18000psi...typical of handgun chambers.  There is no such compressor, so it must be developed from scratch.

The compressed Martian air is given an appropriate dose of hydrogen and then injected into the Sabatier.  What comes out is a mixture of methane, water vapor, surplus carbon dioxide, and a tiny bit of hydrogen, along with other constituent gasses on Mars.  The first task is to get the water out, which happens in a distiller.  The distiller needs no refrigeration, as the record high on Mars is about 11deg.  In fact, it may even need heating because of water's tendency to freeze.  Once the water is out, what's left goes to the first stage of the liquifier, which will condense out everything but the methane and hydrogen.  The second stage of the liquifier liquifies the methane.  The hydrogen is extracted from the vapour and run back into the Sabatier either in the fridge, or in the storage tank, where it will occupy the bubble in the top.

A typical cryocooler operates by running a helium compressor of the Copeland Scroll type.  Helium is an excellent refrigerant with a really high specific heat ratio (aka. gamma) and low heat capacity (meaning it can change temperature quickly.)  The compressor is in the vertical position and is oil flooded.  80% of the adiabatic compression heat is removed by the oil, while the remaining 20% stays with the helium, which is now inconveniently entrained with little oil droplets.  After going through a heat exchanger (water or air cooled) it goes into an oil separator, which uses a big silica cotton puff to gather the oil droplets up and drain them to the bottom.  A charcoal adsorber deals with the vapours.  This is important because impurities can freeze in the cold head and cause it to go on strike.  The cold head uses a displacer piston to expand the helium, leading to efficient adiabatic cooling.

Um...perhaps an oil flooded compressor is a bad idea.  The oil can freeze on Mars, and it means having yet another fluid to bother with.  TAI (http://www.techapps.com/images/03CECPaper.pdf) has a better idea: use a two stage scroll with intercooling so that 100% of the heat is removed by the helium, and the compressor can stay dry.  Copeland Scroll parts do not rub against each other, they press, forming a good enough seal between the compression parts.  This makes the compressor a tad more complex, but everything else having to do with it as complex or simpler.  The radiator, instead of having an oil loop and a helium loop, has two helium loops at different pressures.  The oil separator is replaced by a tiny filter to eliminate wear particles, and the adsorber, if it is needed at all, can be made much smaller.

During the trip to Mars, looking after the hydrogen, especially if it is in your boosters ascent tanks (like it is on Mars Challenger) is also rather difficult.  Fortunately news from the Hershel Planck mission (http://www.rssd.esa.int/herschel/Publ/1998/cryo98-fp-bc.pdf) shows that this is relatively easy and flight proven.  Because the ISRU application is not vibration sensitive, we don't have to get fancy with J-T sorption stuff and 3He diffusers...whatever all that is...  Also liquid hydrogen may be cold, but not _that_ cold.  Cryomech's pulse tubes are good enough.  They are also compatible with the same compressors as the liquifier cold heads.

So, during cruise, we run the same compressor as we will on the surface, but with a different type of cold head better suited to LH2 tempuratures.  With that, we don't need to get as fancy as Herschel with the insulation, and our tanks are built more for the requirements of a sample return booster rather than a cryogenic space telescope.

With basic ISRU, one of the difficulties is caused by the fact that you are likely going to be bringing along more hydrogen than you will have final propellants...by volume, that is (bulk oxymethane propellants are over eleven times as dense as liquid hydrogen.)  This leads to juggling tanks and figuring out how to store propellants without mixing oxygen and something that could explode with it in the same room.  I recommend storing water, the intermediate product from the Sabatier reactor.  It's the easiest thing to store, Mars Challenger uses its hover propulsion system tanks.  In fact, the hydraulic system water tanks on the Shuttle used to be satellite hydrogen tanks...although they're not using exactly the same tanks, like mine.  If you're trying to solve a piloted missions ISRU problem, do be aware that storing water in an ex-hydrazine tank is not a good idea for potable supplies.  Hydrazine is well... Yuck!...actually, it's Jolly Rogers type stuff (typical WHMIS, HazMat, DG symbol...you might notice it on your cleaning chemicals at home.)

That's about it...see easy as  Shocked, enjoy!
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