The latest news from ESA/NASA is that the SOHO reaction wheels and thruster repairs/modifications are back on schedule for a Thanksgiving (23 Nov) launch. This date should be considered very likely.

However, there may be a problem with the Centaur upper stage of the launch vehicle. With a November launch there will be a long delay (about 70 minutes) between the first and second burn of the Centaur. Three tests were just run with the Centaur failing to perform properly on one of the three. That is the extent of my knowledge, but one must assume that a 1/3 chance of a mission total failure would be cause for concern. We will learn more in coming days.

Status report on SOHO launch plans

There was a SOHO launch readiness review on Monday 16 October at ESTEC. The review was for the ESA/NASA "board" . . . The SWT/PIs were all present. Prior to the review itself, there was an executive meeting of the SWT to review instrument status and discuss the SOHO problems. The topics included:

SOHO reaction wheels. The vibration that was discovered in reaction wheel #3 before November 1993 was finally investigated in June/July of 1995. It was found that in addition to the bearing spacer shape error that caused the vibration, the bearings were dry - i.e. no oil. The other reaction wheels were inspected and found to be dry. If the #3 wheel had not failed from a combination of problems, all the wheels would have failed before reaching L1. A panic repair program was instituted leading to rebuilt wheels ready to install in the spacecraft on about 20 October. . .

Thrusters. There was a problem discovered in testing caused by vapor lock in the thrusters depending on the thermal state of the thrusters from prior burns. A change was made to the hardware to prevent the dangerous condition in the automatic sun finding mode and changes will be made in the flight software to avoid the situation in normal operations.

Centaur second stage relight problem. The launch vehicle, an Atlas Centaur combination with an Atlas first stage and a Centaur second stage will be used. Actually the Centaur has two parallel engines. Due to orbit requirements for injection into the transfer orbit to L1, the Centaur stage will be fired twice, once to get into low Earth orbit and again, some 78 minutes later to boost into the transfer trajectory. The duration of the coast depends on time of year with a minimum of c. 10 minutes in Feb. growing to nearly 100 minutes in January. It is apparently favorable or not lunar gravity purtabations that make the difference. The type of Centaur used has worked ``hundreds'' of times with a less than 30 minute delay between two firings. . . A simulation test was recently run where Centaur engines were heated as if just fired, then relit after a delay. The heat from the first burn diffuses to the valves and pumps and can cause a vapor lock if the engine is not cooled enough before firing. About 4 of 6 tests failed at the 90 minute delay spec. 4 or 5 tests worked OK at 78 minutes. Since the repeatable failures occur with a 15% longer delay than is required there is concern that there is too little margin. . .

The totality of the problems led the SOHO instrument PIs to a joint conclusion that without further verification of the wheels, the centaur problem, and the software related problems we do not believe SOHO is ready for launch. . .

I am greatly concerned that the last minute rush to launch has led to a situation where normally very carefully people may have managed to convince themselves that everything is actually OK whereas there is not real evidence to support this conclusion. It may very well be the case that SOHO will launch on Thanksgiving and will work flawlessly for the designed six years. I believe that if it does, the decision will have been OK more because of luck than considered engineering judgment.

I have joined with the other SOHO PIs in a recommendation to delay the launch until March unless a satisfactory answer is found for these problems. . .

Final KSC AFT for the MDI Instrument

The MDI activities performed during the final certification AFT verified the correct operation of the MDI instrument after reintegration of the spacecraft reaction wheels and CAE electronics. In addition, two additional tests were performed to demonstrate that the correct procedure had been established to recover from the MDI high rate ISS mode (jitter mode), and that the front door mechanism was functioning correctly after replacement of the MDI front door gearbox cover. . .

The MDI observation periods were both run with the MDI stimulus telescope and the front door open. The focus and light transfer tests results were nominal. . .

The MDI instrument is considered ready for launch pending review of the MLI and final inspection prior to spacecraft encapsulation.

SOHO launch status

Well, it now looks like the SOHO launch will be at about 2 AM EST on 23 November 1995 (Thanksgiving), ready or not.

There are still outstanding problems but they are being systemmatically solved or glossed over. Let's hope for good luck and get on with preparations . . .

With this schedule MDI will open its door just before the winter solstice and SOHO will reach L1 by April Fool's Day.

SOHO Prelaunch Science and Spacecraft Briefing Set for Oct. 31

The upcoming Solar and Heliospheric Observatory (SOHO) mission will be the subject of a prelaunch science and spacecraft briefing scheduled at 9:30 a.m. EST, Oct. 31, 1995 from NASA's Goddard Space Flight Center, Greenbelt, MD.

SOHO is a project between the European Space Agency (ESA) and NASA, and is scheduled for launch aboard an Atlas IIAS launch vehicle from Cape Canaveral Air Station, FL, on Nov. 23, 1995.

Participants for the briefing will be: Dr. Roger Bonnet, Director of the Scientific Programme, ESA Headquarters, Paris; Dr. Wesley Huntress, Jr., Associate Administrator, Office of Space Science, NASA Headquarters, Washington, DC; Dr. Vincente Domingo, ESA SOHO Project Scientist; Dr. Art Poland, NASA SOHO Project Scientist; Dr. Richard Harrison, Principal Investigator, SOHO CDS Instrument; Dr. Phillip Scherrer, Principal Investigator, SOHO MDI/SOI Instrument.

Reporters covering the briefing from NASA Headquarters, participating NASA Centers and ESA Headquarters will be able to participate in the 2-way question-and-answer session.

Status update

Reaction wheel #5 was opened last week. It was not perfect. In fact both the upper and lower bearings were damaged. There are pits in the ball races, one per ball. It is described as consistent with having been dropped about 4cm. There were some particles in the oil that are consistent with the pits.

There are a number of arguments that since this wheel was damaged it is not representative of the 4 that are in SOHO so, no problem, we can go ahead with the launch. There is no confirmation that it was actually dropped and the others were not.

Some of us are quite concerned. My impression is that people are looking for a reason to be able to disregard this test result. . .

Meeting with R. Bonnet

This morning, after the Pre-launch Press Briefing, we made use of the occasion that four PIs were at GSFC and Roger Bonnet was here, to hold an informal meeting, that gave the opportunity to the PIs to voice their concerns on the readiness of SOHO for launch.

Present in the meeting were: J. Kohl. G. Brueckner, R. Harrison, P. Scherrer, D. Michels, P. Lemaire, R. Bonnet, D. Dale, F. Felici, W. Wagner, G. Withbroe, K. Sizemore, W. Worrall, A. Poland and myself.

At the meeting the PIs exposed their concerns about the various late troubles in the spacecraft and the operation . . . the reaction wheels were presented as the single major concern at this stage, particularly after knowing that anomalies have been observed in wheel#5 when it has been open. . .

Report on the Ground System Compatibility Test, payload part (GSCT#4B)

The test started at 14 hours, October 30th,and ended at 18 hours, October 31st.

With exception of minor anomalies the test has been completed to the entire satisfaction of the participating PI representatives at the closing meeting. . . None of [the anomalies] is launch critical.

The ground system and spacecraft demonstrated full ability to operate the SOHO payload. The flow of commanding and data distribution has been remarkably smooth, and the experimenters were able to send large amounts of commands and to upload software without problem.

Experiment "Ready for Flight"

Dear Principal Investigator, At the meeting on 16 October 1995 at ESTEC you confirmed to ESA's Director of Science that your experiment was ready for flight, with the exception of two issues, i.e. the command interface and the ground segment capabilities.

- In the meantime, investigations have taken place at KSC, and the ``AFT'' run confirmed that the command interface issue was understood and could be closed satisfactorily.

- GSCT-4 has also confirmed that the ground segment performances and compliant and can support the mission.

I therefore ask you to reiterate your readiness statement and confirm in writing by not later than 3 November 1995, 14:00 hrs European time (input to D/Sci at KSC) that your experiment is "ready for flight".

RE: MDI readiness for launch

This memo is to inform you of the current status of the Solar Oscillations Investigation which includes the Michelson Doppler Imager experiment which is part of the Solar and Heliospheric Observatory mission.

To the best of my present knowledge, as of this date, the MDI flight instrument is ready for launch.

However, from the reports I have seen and presentations I have witnessed I do not believe the SOHO mission as a whole has been demonstrated to be able to provide an environment sufficient for MDI to obtain the prime science data required for SOI.

Summary of 3 November conference call.

I just finished a 2-hour 7- or 8- site conference call which was the ESA/NASA SOHO flight readiness review meeting. . .

The agenda included: a review of the flight worthiness of the 4 reaction wheels presently installed in SOHO; the review of the Centaur post-coast phase relight concerns; the review of GSCT-4 A&B; the review of the status of the new procedures for solar panel and over/under thrust contingencies; the final review of all payload items; a review of all other outstanding S/C and launcher issues, etc. . .

The conclusion was to proceed with all actions that are necessary to enable a launch on 23 November.

. . . After the initial discussion about the wheels, which was moderated by Bonnet, with I felt a very careful procedure and ample opportunity for all to aks questions and get responses, there was general agreement that the present 4 wheels are OK for flight. . .

I now believe that the risk to the SOI science program from the wheels is less than the risks would be if we waited a half year or more. . .

We should not however think there is no risk. If one of the wheels fails we should promptly decide the best observing and ops sequences for the best science from a likely short mission since the wheels on SOHO now do seem to be all of the same statistical family.

SOI/MDI weekly update

All is still on track for a 23 November launch. The SOHO web page (http://sohowww.nascom.nasa.gov) shows the current countdown as: Countdown: 09 days 11:57:43 to LAUNCH

The plan is to turn on the MDI CCD heater at about hour 10. The MDI DEP and IP checkout will begin on day 4 with first light set for just after the mid course correction on about day 20.

So, for the Thanksgiving launch look for a first light announcement on about 15 December, \xb1 .

We will then do some initial calibrations and operational checkout over the next week. Then a break while other instruments have priority, then we begin calibration on about 2 January. The first science data is expected in February.

Several of us will be in Florida to watch the launch. . .

Launch Viewing

We are arranging a SOHO launch viewing session in the HEPL Conference Room and/or the Boxtop, beginning at about 9:50 PM on Wednesday Nov 22 and continuing for about 2.5 hours. If people are interested we could turn it into a potluck party for staff and families. Of course reschedule dates are always possible: they recur at approximately 24 hour intervals. Margie and I are handling logistics, so let us know if you are interested.

Government Furlough and the Web

The Kennedy Space Center World Wide Web server which is usually at this address is temporarily offline. It has been replaced with a small battery backed up computer bearing this message. The US Government has shutdown all non-critical services and the NASA Civil Service employees which normally run the server have been sent home on indefinite furlough. We hope to resume this service to you in the very near future.

Launch status

Well, here it is just 05 days 08:52:41 to LAUNCH and all is still on track.

SOHO is on the Atlas and the last minute early ops software for contingencies has been dealt with. . .

There are (were) plans for launch viewing, tours, briefing, etc on Weds. Those plans are all cancelled pending a restart of the government, except for the launch viewing itself. . .

SOHO Uplink Information

We regret to inform you that the NASA Kennedy Space Center WWW server where the Expendable Launch Vehicle Homepage resides has been taken down due to the US Government temporary shutdown.

Fortunately for NASA and the European Space Agency (and others involved), NASA has elected to consider civil servants who are working on SOHO to be ``essential,'' and therefore the majority of Expendable Vehicle operations are proceeding at least for now.

Thanks to Netmind, Inc., provider of the free internet ``Robot'' reminder service, we are able to provide you with a brief status of the SOHO launch preparation . . .

"ELV Launch Pad" back online!

I wanted to inform you that all NASA employees have returned to work, and the Kennedy Space Center World Wide Web Server (where the ELV Launch Pad is kept) is now back online. . .

Thank-you for your patience through the government shutdown. . .

URL for Launch Information

NASA is back on-line! If you want to see updated information for the next launch (ours!), go to http://www.ksc.nasa.gov/elv/DOCS/next_up.htm

5..4..3..

Coverage of the expected SOHO launch tomorrow night will be carried on two separate channels, NASA Select, and a special satellite channel purchased by ESA with additional commentary. Stanford cable will attempt to pull in both channels, and we will set up monitoring of both, one in the HEPL Conference Room and one in the Boxtop. Most everyone has expressed interest in being here for at least some part of the coverage (NASA coverage begins at 9:30 PM and the ESA coverage will continue until 2 AM). Fizzy beverages will be provided and maybe pizza if people wish. If people would like to bring additional munchies or libations to share, that would be great. Margie and Lup are setting up, bless their souls. Scott will arrange to have a continuing display of the MDI housekeeping data direct from the EOF in the Boxtop (as I understand it the power is on during launch!). . . If we are going to videotape both channels we will need an additional VCR. Any volunteers?

SOHO launch postponed

The launch of AC-121 with the SOHO Spacecraft was scrubbed at 10:45 PM EST tonight, just prior to tower rollback, due to the malfunction of an Atlas booster precision regulator. The precision regulator provides reference pressures to control the thrust of the booster engines. The regulator will require removal and replacement and a failure analysis.

The next launch attempt will be early on the morning of Tuesday Nov 28. If that attempt is missed the next (and final) launch attempt in this month's window will be on the morning of Saturday Dec 2.

Re: SOHO launch

Thanksgiving 1995 was a big day for flightless birds.

Gobble, gobble.

Update of the SOHO launch campaign

Today, at 18:30 hours at the SOHO EOF, NASA GSFC, we had a telecon with the SOHO Project Manager, Fabrizio Felici. During this telecon we were informed that:

- Lockheed-Martin has found the flaw in the precision regulator. The diaphragm of the regulator where the hole was found is made of 4 plights of Mylar-A. In the regulator that failed, the first and fourth plights were polyvinylfluoride, not Mylar-A. The strength of the polyvinylfluoride is 7-15 KPSI, as compared with 20-35 KPSI for the Mylar. This appears to be the reason for the failure.

- As they do not know where the substitution of the material took place, they are going to disassemble all regulators in our Atlas (and in the one that comes after ours). An investigation in order to find from where this material came from is under way.

- As of today afternoon (November 25) there is no Mylar-A material available at their Conestoga Park facility. So they are still looking for it, and tests to assess the quality will be made before rebuilding the regulators. It is not clear if the new regulators are going to be tested in hot-firing with an engine. NASA and ESA are strongly recommending to do so. . .

- The earliest possible date for the launch is now Saturday, December 2nd. The window for that day is 51 minutes long, from 2:34 to 3:25 am EST (07:34-08:25 GMT). In order to meet this launch date, the Mylar-A should be available tonight or tomorrow morning.

- Launch dates after December 2nd may conflict with the launch of NASA GSFC's XTE (X-Ray Timing Explorer), currently scheduled for December 4th on a Delta-2 . . .

SOHO status 11/27/95 (launch forecast: 3 dec 95 ~0230 EST)

We just finished a teleconference (at 6:45 EST) between the EOF and KSC, to brief everyone about the status of the upcoming launch. In brief, the most likely launch date is currently Sunday 3 Dec . . .

We heard details of the scenario from several points of view:

Weather: The current forecast for the weekend is very good. A cold front is approaching southern Florida, scheduled to hit late Tuesday or early Thursday. By Friday, clear skies and no winds are expected -- very good launching weather. . .

Rocketdyne was able to find some Mylar over the weekend, and is rebuilding both the sustainer and booster regulators. They are promising delivery by noon on the 29th (Wednesday) for the sustainer regulator, and on the 30th (Thursday) for the booster regulator, but ``will try'' to get both regulators delivered by Wednesday.

Both regulators *will* be hot-fired on their test rig, for 20 seconds apiece, before delivery. The first one happens tomorrow. If both are finished, both firings will happen in quick succession.

An engineering review board is attempting to figure out how the PVF got in. They're also evaluating the other allegedly Mylar components in the rockets, to see if they need replacement.

If the Rocketdyne parts are delivered by Wednesday, Lockheed can have the rocket ready for a Saturday morning launch. If they're not ready until Thursday (the 30th), then the launch will be delayed one more day (for a Sunday morning launch).

Range can support a launch on the morning of the 2nd (Saturday) through 4th (Monday), but there are possible conflicts thereafter.

Current most likely scenario: We're planning for a Sunday morning launch. On Friday (Thursday for a Saturday a.m. launch), SOHO will be switched on (just the S/C, not the instruments) for a comm check. CEPAC will *not* be pumped down again -- the vacuum in the instrument is still ``good enough''. The thrusters will be put back on the launcher on Thursday or Friday. . .

Status

I just came back from the 4 PM telecon with NASA, ESA, LMSC, etc. Things are going well for a Sat AM launch. They have the regulators assembled (almost) and have one ready to ship. The booster regulator will be tested later today and will be on an airplane at 11PM or as late as 2AM to arrive at KSC by noon tomorrow. If they are both here by noon they can keep the schedule for the Fri. night launch. . .

SOHO Launch Status

I have just returned from a series of reviews at KSC concerning the launch status of SOHO. . .

SOHO is READY FOR LAUNCH at 2:34 AM EST on Sat 2 December.

There was some discussion, but that is the answer.

Prior to the Flight Readiness Review there was a briefing for Bonnet and then a detailed (2.5hr) review of the pressure regulator repair. All involved feel that the problem was properly dealt with. The problem was identified as a combination of individual human error and a failure of material controls. There will be discussion for some time about how such things can be prevented in the future.

The conclusion is that we were very very lucky and that the repairs are OK. . .

The mood at KSC is quite good. The weather is perfect. The S/C is ready. The Atlas is ready. Let's see what happens this time.

SOHO Launch rescheduled

The SOHO launch is now officially on for 11:34 PM tomorrow (Friday) night. Lots of us will be watching in the HEPL conference room on the huge new TV that Mike got, and you (and your families) are all welcome to join us. The coverage begins at 10 PM. If you are planning to come, I suggest you notify Margie so that we can arrange to phone you if there is any last-minute change of plans. I realize that almost never occurs, but you never know.

Re: Launch view party

Please do have a good time tonight. I know we will be doing the same.

I will be at the press site after launch to brighten Europe's morning...

SOHO successfully launched

SOHO was successfully launched into Earth orbit at 08:08 UT this morning, Dec. 2, 1995, and successfully injected into transfer orbit at 09:34 UT. It is on its way!

SOHO is away

SOHO was launched at 08:08 UT 2 Dec 1995.

It was injected into the transfer orbit at 09:34 UT. Due to a slight delay launch was just 2 minutes before the end of the window for today. Shortly after 10 UT the Centaur upper stage was separated and SOHO was on its way. Telemetry was picked up by DSN Madrid just 30 seconds before separation, just to keep up the level of interest... The orbit looks good. The solar panels opened and locked. Pointing is nominal. The substitution heaters were turned on as planned. MDI went as low as 10 degrees which was well above our minimum spec and is now resting at 17 degrees. We will power-up MDI in about 4 hours to turn on the CCD heater. The CCD is now running at about -74 degrees C which is about as expected.

Now the real fun begins!!!!

Interim EOF update

. . . Cheers from EOF-land (lots of smiling, if tired faces)

NASA PRESS RELEASE

The unmanned Atlas rocket carrying the spacecraft blasted off at 3:08 a.m. from Cape Canaveral Air Station, more than a week late because of rocket problems.

The Solar and Heliospheric Observatory, called Soho, should reach its final destination in four months -- a point nearly 1 million miles from Earth and 92 million miles from the sun. The gravitational pulls of Earth and the sun cancel each other at this point.

There, Soho will peer continuously at the sun and send back data for two years, longer if NASA and the European Space Agency can afford it. It is considered the most complex observatory ever built to study the sun's deep interior as well as the corona, its outer atmosphere, and the ever-expanding solar wind.

``These experiments provide a new and really exciting, we believe, chance to journey from the center of the sun all the way out to the surface,'' said Philip Scherrer, a Stanford University physicist in charge of one of the Soho instruments. ``Soho will see the conditions out to the farthest limits of the heliosphere.''

Comet SOHO

From Jonathan's Space Report No. 266, 1995 Dec 3, Cambridge, MA:

The SOHO satellite was launched at 0808 UTC on Dec 2 by Atlas Centaur AC-121. SOHO, the Solar and Heliospheric Observatory, is a European Space Agency science spacecraft developed in collaboration with NASA. The Lockheed Martin Atlas IIAS took off from Pad 36 at Cape Canaveral; the Centaur second stage made an initial burn to enter low parking orbit of 175 x 183 km x 28.8 deg and then a second burn at 0935 UTC to insert SOHO onto an interplanetary trajectory towards the Earth-Sun L1 Lagrange point, 1.5 million km from Earth in the direction of the Sun. The Centaur separated from SOHO at 1009 UTC; around 1045 UTC diffuse emission (reported as a possible new comet!) was seen by observers in the Northeastern US which may be associated with Centaur venting. The Centaur was inserted in an orbit with an apogee of 1.15 million km, and is likely to end up in solar orbit after a couple of revolutions because of perturbations. . .

SOHO carries telescopes, spectrometers and coronagraphs to study the atmosphere of the Sun, and particle detectors to study the composition and state of the solar wind. Unlike earlier solar observatories, however, SOHO also carries instruments to precisely measure oscillations of the Sun, which can be used to study the interior structure of the Sun - a technique called helioseismology. The 1850 kg spacecraft was built by Matra Marconi Space. . .

And after Launch . . .

MDI is ON

MDI was turned on about 3 hours ago. It is working well. The CCD heaters are bringing the CCD up to a warm temperature to keep crud from condensing during the next two weeks or so. Further MDI testing will proceed over the coming week. Our first light is still scheduled for just before Christmas.

The spacecraft is having the expected number of minor problems. The net effect so far is to slip activities several hours.

Special thanks and congratulations to the EOF team for a job well started!!!

MDI First Light!

The MDI front door was opened at 17:49 UT today, and a series of 8 test images were taken and transmitted. Our very first full-disk image of the Sun from space can be seen on the SOI Web home page, http://soi.stanford.edu, and the data files themselves, like all other data in the SOI data system, are available for export via the Web.

The alignment offset of 174 arcsec is almost exactly what was predicted due to gravity unloading.

This story to be continued . . .

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Last Modified: 15 February 1996