Space Access Update is Space Access Society's semi-weekly publication. Space Access Society's goal is to promote affordable access to space for all, period. We believe in concentrating our limited resources at whatever point looks like yielding maximum progress toward this goal.
For the moment, our main focus is on supporting BMDO's "SSRT" (Single Stage Rocket Technology) program, DC-X and its planned-but-not-yet-funded followon, SX-2. Space Access Update is thus for the moment largely about the technology and politics of DC-X and SX-2.
We anticipate a change of focus in a couple of months, if all goes well. Once SX-2 startup funding is (with your help!) assured, we plan to begin working on establishment of a healthy second X-rocket development track at NASA, and on getting development of suitable engines started for the fully reusable orbital ships that should come after SX-2 and NASA's X-rocket.
With luck and hard work, we should see one or more fully reusable SSTO testbeds flying to orbit toward the end of this decade, with production prototypes entering test a couple of years after that. Join us and help us make this happen.
Henry Vanderbilt, Editor, Space Access Update
[For more info on Space Access Society, write us at 4855 E Warner Rd #24-150, Phoenix AZ 85044, or email hvanderbilt@bix.com.]
[Editors note -- For those of you seeing this for the first time who need a bit more context, look for the subsequent post titled "DC-X Background".]
We've had an education in the care and feeding of large cryogenic liquid tanks over the last week, mostly due to our having supplied a somewhat incorrect explanation of the basic facts we'd gathered on DC-X's slow throttleup problem at the start of its third flight, back on September 30th.
We've also dug out a few new facts. Here's the story, as best we understand it now:
Cryogenic liquid propellant tanks can have a problem with "geysering", gas bubbles forming in the propellant feed plumbing at the bottom of the tank then erupting into the main tank, with the cryo liquid then slamming back down into the plumbing. In a large tank full of relatively dense liquid, "geysering" can be forceful enough to damage plumbing, rather like a bad case of water hammer in a house's pipes.
Geysering happens because the propellant feed plumbing at the bottom of a cryo tank tends to be the warmest region, because of the plumbing's higher surface area to volume ratio and its direct connection to outside world heat sources.
Apparently the standard cure for geysering is to bubble a small amount of helium gas into the cryo liquid at the lowest point the liquid normally reaches with engines shut off, near the propellant cutoff valves in the engine feed plumbing. This circulates the cryo liquid better than convection can; it may also provide some cooling effect as the cryo liquid evaporates into the helium bubbles. The net effect is to keep the propellant feed lines cold enough to prevent geysering.
Anti-geysering helium feeds in a rocket would normally be cut off long enough for all bubbles to clear out of the propellant feed lines and intake area; this waiting period is called a "tank sweep".
On September 30th, DC-X's liquid oxygen (LOX) tank helium line contained some sort of contamination, enough so that when the helium valve was closed, some helium continued to leak through. When DC-X's engines were started there were still helium bubbles in the LOX feed lines and LOX line inlet region. These helium bubbles caused the uneven and delayed engine throttleups that lent a certain excitement to DC-X's first few seconds off the launch stand.
The cure has been to replace the valve in question and to install two more valves in series with it, in order to ensure that when they close those valves, helium flow will in fact stop.
DC-X's fourth and fifth flights look like they're on for tomorrow, Wednesday 10/20/93 at 10 am Mountain time, and Saturday, 10/23/93 at 2 pm Mountain time. This will be the long-awaited "Turnaround Test", a demonstration of the fast turnaround between missions possible for a properly designed small-crew reusable rocket.
They may also be DC-X's last flights for a while, if not forever. (See the following section for details; briefly, current DC-X funding has run out.) There has been some speculation that in light of this, the test program might be fast-forwarded to do the end-for-end "flip" maneuver on Saturday, but from what we hear this simply isn't practical.
What we hear is that before the "flip" or any other radical high speed/high angle-of-attack maneuvers, the DC-X team would need to take the results of the early low speed tests still underway, use them to plan several weeks of wind-tunnel tests, then feed the results back into reprogramming the flight control system's "control laws", its computer model of how the ship will react to control inputs under various conditions. This is a standard part of flight-testing any fly-by-wire aircraft, and there's no practical shortcut.
What DC-X will be doing these next two flights, according to MDA:
Wednesday: DC-X will fly vertically to 1200 feet, then follow a curved path to 2600 feet, travelling laterally 1050 feet and going through an angle-of-attack range of 0 to 70 degrees. (Angle of attack or AOA or "alpha" is the difference between an aircraft's actual direction of motion through the air and the direction its nose is pointing. An AOA of 90 degrees would mean DC-X is travelling sideways through the air.)
DC-X will then reverse its direction of flight and climb another 250 feet while transitioning 700 feet sideways, ending up directly over its landing pad, 350 feet from the launch stand. It will then descend vertically and land, approximately 132 seconds after takeoff.
Saturday: Again a curved ascent, this time reaching 4350 feet and covering 1150 feet laterally. DC-X will then reverse course and move laterally 950 feet, holding at 4350 feet altitude, then reverse course again for 150 feet to center itself over the landing pad, then descend. Total flight time should be roughly 135 seconds.
We reported last week that DC-X FY '93 flight test funds were running out, that absent new funding before the end of October the program would have to shut down, and that BMDO had not yet provided any money from their "Continuing Resolution" temporary FY '94 funding. (The US Federal government's fiscal year starts on October 1st, and if the new budget is not yet passed, Congress will vote a "continuing resolution", a temporary continuation of funding at last year's levels. DOD is currently operating under such.)
It has since become clear that BMDO doesn't intend to spend another dime of their own money on DC-X, absent new Congressional funding or specific orders from higher up. We're unlikely to see new funding in time, and orders from higher up in the chain of command would have to come from Administration appointees in the Pentagon, or from the White House itself. Neither of these places has recently shown any detectable support for SSTO.
BMDO's position is actually not all that unreasonable, given that their new mission is strictly limited to providing ground-based theatre missile defenses, while their overall budget has been sharply cut. SSTO tech development simply isn't their job anymore, and they'll need every penny they have to do the job they've been ordered to.
If new funding does show up, BMDO would be happy to apply it to DC-X flight test -- apparently they have nothing in particular against SSTO. But it's not at all clear yet whether new funding will in fact arrive in time.
Chances are that after this coming weekend, DC-X and its ground support gear will be mothballed for a while, and the DC-X crew assigned to other jobs or laid off. And there's nothing to be done about it (barring some surprise inside maneuver) but to keep up pressure on the Congress so that eventually there will be new funding to resume DC-X flight test and get a followon design underway. [unprofessional expletives deleted.]
[SSRT is the Single Stage Rocket Technology project, DC-X/SX-2.]
The leading argument used by SSRT's behind-the-scenes opponents in recent weeks has been that a Single Stage To Orbit spaceship requires too many advances in lightweight structures and high-efficiency engines to actually fly soon, that SSTO is so risky it requires a decade or more of expensive research before we can even think of trying to build one.
A thought experiment: An SSTO using liquid oxygen and liquid hydrogen for propulsion needs to be somewhere between 89% and 91% propellant by weight at takeoff. The optimists say 89%, the pessimists 91%. The difference depends mainly on your assumptions about engine efficiency and air drag during ascent. For the sake of argument, let's split the difference and call it 90%.
Now 90% is obviously an impossibly high takeoff propellant fraction, right? Well, let's take a look at Shuttle, a design laid out twenty years ago. Now SSTO versus Shuttle propellant fractions is admittedly an apples-and- oranges comparison, but it'll give us some sort of a baseline.
Hmm, orbiter and payload, external tank, solid booster casings, divide into a Shuttle stack's 4.5 million pound liftoff weight, and what do you know -- the twenty year old Shuttle design is nearly 87% propellant at takeoff.
Twenty years later, and these people say we can't do three percent better?
This would be laughable, if the result of this nonsense wasn't all too likely more years of neglect for SSTO. If these people prevail we'll get another decade of study-it-to-death aerospace welfare, despite the nation's crying need for affordable launch.
- Henry Vanderbilt
For the last week, House and Senate Armed Services Committee staffers have been doing the advance work for the Defense Authorizations conference. They've been coordinating with their Appropriations counterparts -- when the Authorizations conference finally happens, which should be any day now, the Appropriations conference will follow closely.
The bad news is that the anti-SSTO space staffers (most on the Senate side and some from the House) have beaten down attempts to preserve the favorable House DOD Authorization language that provides $79.88 million and a move to ARPA for the SSRT (DC-X/SX-2) project.
Going into the actual conference, these staffers' draft compromise bill will lump SSRT, NASP, and "Spacelifter" together in one $40 million line item. You may recall this is almost exactly what first came out of the Senate Armed Services Committee, before the full Senate cut out the SSRT/NASP/"Spacelifter" combined line item entirely.
This is not good. Money aside, lumping SSRT in with NASP and "Spacelifter" will kill it as an independent program. This is a recipe for once again studying the launch problem to death, not for an aggressive X-vehicle SSTO development effort.
The elected Representatives and Senators still have the final say, but they have too much to do and far too little time. The vast bulk of the DOD money bills will pass as drafted by the staffers. If we want something done about our piddling little detail (we're talking about .03% of the total DOD budget) we'll have to make sure the elected types hear us over the clamor from all the others who want their ear.
It's probably too late to convert anyone not already in favor of SSRT, this year. We need to go back to our friends and let them know we have a problem that needs fixing; we have to convince some key neutral figures to stand back and let our friends fix things.
This is, no fooling, it. It should be all over but the shouting by sometime next week. [And not a moment too soon! Ed.]
For what it's worth, one of the staffers opposing SSTO recently tossed off this gem: "SSTO? C'mon, the only people who support that are Trekkies and right-wingers."
The message is: Keep BMDO's Single Stage Rocket Technology (SSRT) program as a separate line item in the DOD budget conference, and fund it at the House Authorization level of $80 million. Don't combine SSRT with NASP and "Spacelifter" and turn it into just another paper study.
Call, write, or fax:
Ron Dellums, House Armed Services Committee (HASC) Chair phone(202) fax address 225-2661 225-9817 2136 RHOB, Washington DC 20515 Patricia Schroeder, HASC Research & Technology Subcommittee Chair phone(202) fax address 225-4431 225-5842 2208 RHOB, Washington DC 20515 John Murtha, House Appropriations Committee, Defense Subcommittee Chair phone(202) fax address 225-2065 225-5709 2423 RHOB, Washington DC 20515 Sam Nunn, Senate Armed Services Committee (SASC) Chair phone(202) fax address 224-3521 224-0072 SD-303, Washington DC 20510 Strom Thurmond, SASC Ranking Republican Member (RRM) phone(202) fax address 224-5972 224-1300 SR-217, Washington DC 20510 Daniel Inouye, Senate Appropriations Committee, Defense Subcommittee Chair phone(202) fax address 224-3934 224-6747 SH-722, Washington DC 20510
If either of your state's Senators are on SASC or SAC Defense (see previous Updates), or your Representative is on HASC or on HAC Defense, get in touch with them too, if at all possible.
"Trekkies and right-wingers", yeah, right.
Win, lose, or (most likely) somewhere in between, to everyone who's taken the trouble to help this year, thanks.
Henry Vanderbilt "Reach low orbit and you're halfway to anywhere Space Access Society in the Solar System." 4855 E Warner Rd #24-150 - Robert A. Heinlein Phoenix, AZ 85044 602 431-9283 voice/fax "You can't get there from here." (hvanderbilt@bix.com) - Anonymous -- Permission granted to redistribute the full and unaltered text of this -- -- piece, including the copyright and this notice. All other rights -- -- reserved. In other words, intact crossposting is strongly encouraged. --