DoD and DoT will form task force to examine issues of using GPS for both civil and military missions.
BMDO flies its first experimental launch since it ceased to be SDIO, a suborbital flight May 23.
Congressional investigators likely to urge NASA to pencil in a second repair visit to Hubble immediately, as a hedge against the public-relations disaster that would ensue if something goes badly wrong in December.
NASA review panel looking at the Hubble repair adds one more issue to its final report: possible problems with mirror contamination from space-suit gases. NASA plans to run some experiments on a July mission to assess the problem.
Hubble imaging finds a small spiral in the core of elliptical galaxy NGC 7252, strengthening the theory that it is the result of a merger of spiral galaxies.
Magellan begins aerobraking, in a plan to circularize its orbit while using only about 8% of the fuel that doing it with thrusters would need (thus doing it within the fuel Magellan actually has). The main worry is whether the money will run out before the lowered orbit can be exploited for better gravity mapping, or indeed before aerobraking is finished -- Magellan managers are trying to find $700k within JPL just to make sure aerobraking can be completed, and another $6M will be needed for two cycles of gravity mapping.
Magellan is being "walked" down into the atmosphere with multiple burns to slowly lower its periapse, because Venus's upper atmosphere is poorly understood. The main concern is temperature limits: Magellan's solar arrays should take 160C, and the antenna dish 180C, for short periods. There are no structural problems, since total drag forces will be only a few pounds. Surface degradation is a bit of a concern; material samples were tested in Earth's atomic oxygen on a shuttle mission last year, but Venus's CO2 atmosphere is not the same. Stability is not a serious problem, since Magellan is aerodynamically stable in the aerobraking attitude (antenna dish aft, solar arrays broadside-on), as predicted by Martin Marietta (spacecraft builders) and confirmed by data from the first passes, and there is aerodynamic damping of oscillations. Magellan's thrusters serve for last-resort control, and are programmed not to activate until attitude drifts 10deg off nominal.
About 700 aerobraking passes are expected to be needed, for a total velocity loss of 1250m/s, reducing apoapse from 8468km to 600km. At the end, a small rocket burn will be made to raise periapse out of the atmosphere. That will be done at about the 80-day mark even if the desired braking has not been completed, because geometry problems with star scans for attitude calibration intervene then.
Magellan started aerobraking with 90kg of fuel. About 10kg total will be used for periapse manipulation, and perhaps 50kg for attitude control during braking. Given aerodynamic stability, attitude control is needed mostly to stop initial drift. "On some passes, the drag on the high-gain antenna pulls the spacecraft into alignment before the thrusters are needed."
Magellan is generally in good health. The X-band transmitters remain incapable of reliably transmitting high-rate data, precluding further return of radar data, but the X-band carriers are still in fine shape and that's all that's needed for gravity work. Gyroscope A-1 was turned off May 3 as it showed signs of imminent failure (B-2 was shut down in 1990 for the same reason), but the remaining two are adequate.
Magellan's planned 200x600km orbit will actually be the best gravity- mapping orbit yet seen. (Earth-orbiting gravimetry satellites generally stay higher to minimize air drag.) The main benefit of the lower orbit will be precise gravity mapping of polar regions; the equatorial areas are well-mapped already, but the old orbit was too high over the poles for good results, and Venus geology is too poorly understood to reliably extrapolate equatorial results to the poles.
Eureca, scheduled for shuttle pickup soon (although the schedule has slipped again because of flawed springs in the turbopumps), has problems. There have been several anomalies seen, the worst of which is that the number 1 solar wing has seen unexpected drops in performance of some of its sections. It is not clear why wing 1 is suffering and wing 2 is not, although there is suspicion that it may be materials failures associated with the fact that only wing 1 got the full battery of pre-launch acoustic-stress tests. Alternatively, wing 1 might have taken some substantial debris hits. ESA is quite interested in finding out what went wrong; the hardware was *supposed* to be good for up to five flights.
A more immediate worry is that the deterioration of wing 1 might cause trouble for the shuttle recovery. The wings have to be folded before Eureca can be retrieved -- Eureca is not equipped to jettison them. There is no evidence at the moment that the wing problem will imperil successful folding, but nobody's certain. The astronauts have practiced a manual folding procedure. A related question is whether the wings could be unfolded again if problems develop; if Endeavour cannot grapple Eureca within 160min of wing folding, the wings will have to be unfolded again to recharge Eureca's batteries before another attempt.
A further problem is that some of Eureca's hydrazine valves are acting up -- three times, a valve has opened inadvertently -- and this could present safety problems if more than one opened (which has not happened). Nobody is quite sure what's going on. NASA has agreed to waive normal safety rules and go ahead with the retrieval anyway.
Eureca has generally met its specs, but it is unclear whether it will fly again. The scientists would like to see more flights, but ESA is short of money for it. Another aspects is that some investigators would like to see destructive testing of some of Eureca's components, to look at long-term space effects on things like the carbon-fiber struts; ESA's current position is "nondestructive testing only".
The latest shuttle problem is bad springs used to retain bearings in the turbopumps. A Rocketdyne inspector rejected a spring, noting that the etched certification mark was on the wrong area of the spring and could weaken it. Another inspector recalled that other springs with the same mistake had been shipped, and the ensuing investigation found one in Endeavour's #2 engine. The engine's turbopump is being replaced, this being the quickest way to get Endeavour ready for flight. (Eureca can't wait forever.)
Engineers are also chasing a more mysterious problem: a loud bang, heard and felt in Endeavour during a fuel-system pressure test. Best guess is that parts in the flexible joints in the fuel feed line can bind during initial pressurization and then snap free as pressure rises; this fits the symptoms, and a borescope inspection reveals suspicious scars on the metal parts in one of the joints. NASA is trying to verify that flight pressure will always free the joints.
Testing underway over the North Atlantic of a novel idea that might compete with comsats for some airliner communications: digital data links using shortwave radio. Shortwave is not very good for voice transmissions, because propagation is unpredictable and noise is high. But digital transmissions, sending data in very short bursts and using ground-based beacon transmissions to pick the best frequency several times a minute, are a different matter. The overall data rates will be much lower than what can be achieved with satellites, but the equipment will be much cheaper (since airliners already have the radios), and the system will be usable in the polar regions where Clarke-orbit comsats are not.
Altruism is a fine motive, but if you | Henry Spencer @ U of Toronto Zoology want results, greed works much better. | henry@zoo.toronto.edu utzoo!henry