Bus Driver
Cunning Linguist
Chris’ post, this morning -
Yesterday was another good day with the cryocooler release, momentum flap flipping into position, and getting the folded sunshield uncovered. Today we’ll extend the midbooms which are the sunshield spreader bars that stick out on either side of the spacecraft. A few words on each of these…
The science instruments are on the back side of the telescope and the entire assembly (mirrors, structure, instruments, etc.) will passively cool down to about 40 K (-390 F) because they will be shaded from the sun and facing deep space. This allows them to see infrared light because you can’t be glowing in the same wavelength region that you are trying to see. No heat = no glow, so cold is good. However, in some cases we want to see things that can’t be easily seen even at 40K so one of the instruments uses a refrigerator to active cool it down to 7 K (-450 F). That refrigerator is called the cyrogenic cooler, or cryocooler, or just cooler depending upon your mood at the time. Running the cooler takes a lot of power to run compressors which generates a lot of heat. Because of that the refrigerator part of the system is down on the spacecraft bus on the hot side of the vehicle. The cold gas is then transported through long slinky like pipes up along the DTA, which we extended a couple of days ago, to the cold side of the spacecraft where they are connected to the MIRI instrument. The cold gas cause this one particular instrument to get extra cold. The heavy cryocooler compressor assembly had to be restrained to the spacecraft structure for launch, but we want it mechanically isolated from everything else during operation so vibrations that it produces don’t shake the cameras. Yesterday we blew the launch restraints allowing it hang free to get that isolation.
The momentum flap is just a rectangle that is now fixed in its permanent position. It better balances the profile as seen from the sun to minimize the effects of solar wind causing the spacecraft to torque. Any torque imparted onto the vehicle by solar pressure has to be cancelled out by the Attitude Control System (ACS) which causes us to expend fuel. Less fuel = less mission life = bad.
As mentioned yesterday, the sunshield layers are carefully folded and stored for launch on the large UPS arms that we dropped a few days back. Yesterday the launch covers were rolled back to expose the sunshield so the spacecraft is now in the pictured configuration. Today the Midbooms will be extended. They along with the ends of UPS pallets (the things the sunshield is currently sitting on) form the corners of the diamond shaped sunshield. If things continue to go according to plan we’ll start unfolding and stretching the first sunshield layer tomorrow. I’ll discuss that after NASA announces it.
Keep in mind that everything I put out here is just the baseline plan. We discuss the plan daily and things can change even if there is nothing wrong. A couple days back it was even considered to take a day just to let people catch up on administrative tasks on their systems now that we’re seeing things in flight for the first time. We pressed on because everyone seemed comfortable with their progress. So stay tuned… monitor NASAWebb on Twitter…and enjoy the mission.
Yesterday was another good day with the cryocooler release, momentum flap flipping into position, and getting the folded sunshield uncovered. Today we’ll extend the midbooms which are the sunshield spreader bars that stick out on either side of the spacecraft. A few words on each of these…
The science instruments are on the back side of the telescope and the entire assembly (mirrors, structure, instruments, etc.) will passively cool down to about 40 K (-390 F) because they will be shaded from the sun and facing deep space. This allows them to see infrared light because you can’t be glowing in the same wavelength region that you are trying to see. No heat = no glow, so cold is good. However, in some cases we want to see things that can’t be easily seen even at 40K so one of the instruments uses a refrigerator to active cool it down to 7 K (-450 F). That refrigerator is called the cyrogenic cooler, or cryocooler, or just cooler depending upon your mood at the time. Running the cooler takes a lot of power to run compressors which generates a lot of heat. Because of that the refrigerator part of the system is down on the spacecraft bus on the hot side of the vehicle. The cold gas is then transported through long slinky like pipes up along the DTA, which we extended a couple of days ago, to the cold side of the spacecraft where they are connected to the MIRI instrument. The cold gas cause this one particular instrument to get extra cold. The heavy cryocooler compressor assembly had to be restrained to the spacecraft structure for launch, but we want it mechanically isolated from everything else during operation so vibrations that it produces don’t shake the cameras. Yesterday we blew the launch restraints allowing it hang free to get that isolation.
The momentum flap is just a rectangle that is now fixed in its permanent position. It better balances the profile as seen from the sun to minimize the effects of solar wind causing the spacecraft to torque. Any torque imparted onto the vehicle by solar pressure has to be cancelled out by the Attitude Control System (ACS) which causes us to expend fuel. Less fuel = less mission life = bad.
As mentioned yesterday, the sunshield layers are carefully folded and stored for launch on the large UPS arms that we dropped a few days back. Yesterday the launch covers were rolled back to expose the sunshield so the spacecraft is now in the pictured configuration. Today the Midbooms will be extended. They along with the ends of UPS pallets (the things the sunshield is currently sitting on) form the corners of the diamond shaped sunshield. If things continue to go according to plan we’ll start unfolding and stretching the first sunshield layer tomorrow. I’ll discuss that after NASA announces it.
Keep in mind that everything I put out here is just the baseline plan. We discuss the plan daily and things can change even if there is nothing wrong. A couple days back it was even considered to take a day just to let people catch up on administrative tasks on their systems now that we’re seeing things in flight for the first time. We pressed on because everyone seemed comfortable with their progress. So stay tuned… monitor NASAWebb on Twitter…and enjoy the mission.
