Astronauts are preparing for the third spacewalk of SM4, set to begin at 9:16 a.m. ET (15:16 CEST) today. Today’s activities will include removal of the Corrective Optics Space Telescope Axial Replacement, the installation of the new Cosmic Origins Spectrograph and the repair of the Advanced Camera for Surveys.
Below is one of my favourite pictures, so far, from SM4.
Name: Lothar Gerlach
Title: Head of ESA Solar Generator Section
What is your area of expertise?
I have more than 30 years of experience with solar cells and solar generators.
What made you choose this field?
I wanted to go to northern Germany and I opened a newspaper and found a job. I first worked for a company manufacturing solar generators for ESA. My first project was Spot 1, a French Earth-observing satellite. I designed the electrical network for the solar generator.
Tell us about the challenges of designing the power source for a spacecraft.
A solar generator is exposed. It is, in principle, the subsystem with the most interactions with different spacecraft subsystems and the harsh space environment. We have to survive the launch, we have to generate the power and we are outside. All of our equipment is exposed to radiation, thermal cycling in extreme case up to 230C and down to around -200C and other space hazards (such as debris and micrometeorites). We have to design our solar arrays to be compatible with other subsystems such as the ACS (Attitude Control System) because uncontrolled ACS movement could damage the solar generator.
In general, we also have to permanently improve solar cell efficiencies to reduce cost and weight. The cells constitute about 40% to the overall solar generator cost. Also, the larger the array, the more fuel is required to control the attitude of the satellite. Depending on the mission, we go to extremes - close to the Sun or to deep space. We can design solar generators for going to the Jovian system, but not beyond (because the Sun’s intensity is too low at that distance).
How have Hubble’s solar arrays and the drive mechanisms and electronics performed?
So far, everything is going like clockwork - nothing unforeseen has happened. And we are very happy about it.
How do you feel about supporting what many call the most powerful astronomical tool of our time?
For me, HST was always very emotional because I was involved since the beginning of development. In 1993 and 2002, the dream of every engineer came true for me: I got my hardware back from space and got to inspect it.
This mission brings back memories because you meet up with your old colleagues who were old to begin with 20 years ago; they haven’t aged, but I have. I went from red hair to gray.
Do you have a favourite HST image?
Ultra Deep Field - I’ve used it in my photo collages. Hubble has served as inspiration for me in my art as well. I have created a mosaic of Hubble using solar cells.
Have you worked all of the Hubble Servicing Missions?
What has been the most exciting part of SM4 for you so far?
Launch and Hubble approach. Seeing the old baby - the grown-up baby - back!
What has been the most stressful part of SM4 for you so far?
Lack of sleep
What is next for you?
More work on solar cells. We are currently collaborating with industry partners to design an array for the Solar Orbiter spacecraft that will get as close as 0.22 AU; that’s about one-fifth of Earth’s distance from the Sun.
The NASA briefing will take place today at 6 p.m. ET (0:00 CEST). Watch NASA TV.
Today’s NASA briefing will take place at 5:30 p.m. ET (23:30 CEST)
The participants will be Tony Ceccacci, STS-125 lead flight director, Tomas Gonzalez-Torres, STS-125 lead EVA officer, Jon Morse, director, Astrophysics Division and Preston Burch, HST Program manager.
Spacewalkers Install Final RSU
Fri, 15 May 2009 07:56:11 PM GMT+0200
The final rate sensor unit was successfully seated and installed into place.
Massimino and Good are now working to perform the first half of the mission’s battery replacement work. From the telescope’s Bay 2, they’ll replace the first of two batteries. Good will retrieve the old battery by disconnecting six electrical connectors and unscrewing 14 bolts, while Massimino retrieves the new battery from its stowage location inside the shuttle’s super lightweight interchangeable carrier. He’ll have to unscrew 12 bolts to remove it. The two astronauts will swap batteries at the carrier, and Good will transport the new battery to the telescope for installation, while Massimino stows the old.
Spacewalkers Work on Final RSU Replacement
Fri, 15 May 2009 07:13:36 PM GMT+0200
When attempting to seat the final replacement rate sensor unit, the same issue occurred as before. Without being able to seat the replacement unit properly, they now will retrieve a spare unit and install it in the final slot.
Spacewalkers Replace Second RSU
Fri, 15 May 2009 06:38:47 PM GMT+0200
The second rate sensor unit easily seated into place. The spacewalkers secured it with bolts and installed connectors. They now will replace the final unit by taking the one that would not go into place and try to seat it in the final slot. There is a contingency unit, if needed, but the goal is to use the one that’s newly designed.
Spacewalkers Continue With RSU Replacement
Fri, 15 May 2009 06:11:13 PM GMT+0200
The spacewalkers were not able to seat the second replacement rate sensor unit into place. They now are going to take the third RSU and try to seat it in that same slot to see if that works.
Great news to celebrate both for ESA and NASA yesterday! Two successful science mission launch events took place in one week: the amazing Atlantis launch for the Servicing Mission 4 of the NASA/ESA Hubble Space Telescope and the impressive Ariane 5 launch of the ESA Herschel and Planck observatories. Since the ESA HST team members have also been involved in the development of both satellites, we happily joined, via the web link, the ESA launch team celebrations in Kourou, French Guiana.
This is a great day for science and the public! The 3.5-metre telescope mirror of Herschel at the Lagrange point L2 will join the Hubble 3-metre mirror at low-Earth orbit and both telescopes with new cameras will allow unprecedented views of the evolution of galaxies and stars, the origin of the Universe, black holes and dark matter.
During yesterday’s “orbit shift”, the ESA HST team followed with keen attention the critical events of the first EVA day. After depressurisation of the airlock, two astronauts moved head-forward towards their worksite. Tension rose when the astronauts experienced initial problems in the replacement of the Wide Field and Planetary Camera 2 (WFPC2). An attachment bolt for the camera didn’t want to rotate under the applied release torque of the powered tool. Relief came when the astronaut used a manual torque wrench with applied higher torque. Great to have astronauts in these complex refurbishment tasks! The new Wide Field Camera 3 (WFC3) was then successfully placed and also the next task of this EVA day, the replacement of the Science Command & Data Handling unit (Hubble’s main computer), was successfully achieved. The planned replacement of some HST doors locks, aimed at easing the replacement tasks of hardware in the coming EVA days, posed some challenge. Fitting the new “EVA friendly” locks proved to be difficult in some locations.
Overall, a challenging EVA day of about 7 hours work; the key objectives, the new camera placement and the science data handling unit repair have been achieved. The two astronauts moved back through the airlock into Atlantis for a well-deserved overnight rest. The functional testing during the “planning shift” of both replaced units proved successful and we are now up for a new challenging EVA day 2. As anticipated by the ESA HST team, the replacement operations on the HST telescope caused the solar array wings to slip about 2 degrees from their original position, but it’s nothing to worry about. By design, the applied SADM (solar array drive mechanism) brakes provide limited holding capabilities, mainly aimed for holding the wings in position during the HST observing periods.
Today, astronauts Mike Good and Mike Massimino will conduct the second EVA (or spacewalk). On the agenda will be the replacement of three rate sensing units, part of the important gyro assemblies. The gyro assemblies are vital components as they sense vehicle motion and provide rate data to help aim Hubble precisely for its science observations.
Coming up today (14 May at 5:15 p.m. EDT/23:15 CEST), NASA will conduct a mission briefing. You can watch on NASA TV. Astronauts completed the first EVA (spacewalk) in seven hours and twenty minutes, replacing WFPC2 with WFC3 and upgrading Hubble’s computer, the Science Instrument Command and Data Handling Unit.
Meanwhile, the ESA HST team reports that there was about 2 degrees of solar array slippage during the full EVA day. This is normal and the movement is completely within expected parameters.