Webbs orbit is around L2– a point of gravitational balance on the other side of Earth from the Sun– however it does not live exactly at the L2 point. Right at that point, Earths watching of the Sun would be big enough to considerably lower the amount of power readily available for Webbs solar arrays, without significantly simplifying the cooling obstacles. In addition, when Webbs interaction antennas point at Earth to get commands, they would be blinded by the big radio emission of the Sun in the same direction. Instead, as the diagram indicates, Webb operates in an extremely loose orbit (numerous numerous thousands of km in diameter) around L2, in continuous sunlight and with clean communications with the ground stations. Credit: NASA
On December 25, the Webb team successfully executed the very first of 3 prepared orbit corrections to get Webb into its halo orbit around the 2nd Lagrange point, L2. To hear more about these essential maneuvers, here is Randy Kimble, the Webb Integration, Test, and Commissioning Project Scientist, at NASA Goddard:
In sending out the Webb Observatory into its orbit around the Sun-Earth L2 point, the huge bulk of the energy needed was supplied by the Ariane 5 rocket. After release of the observatory from the rocket, a number of little tweaks to the trajectory are prepared, to reduce the observatory into its operating orbit about one month after launch.
The biggest and most important mid-course correction (MCC), designated MCC-1a, has currently been successfully executed as planned, starting 12.5 hours after launch. This time was selected due to the fact that the earlier the course correction is made, the less propellant it needs. This leaves as much staying fuel as possible for Webbs regular operations over its life time: station-keeping (small adjustments to keep Webb in its wanted orbit) and momentum discharging (to counteract the results of solar radiation pressure on the big sunshield).
The burn wasnt scheduled immediately after launch to offer time for the flight dynamics team to receive tracking data from 3 ground stations, extensively separated over the surface area of the Earth, thus supplying high precision for their determination of Webbs position and velocity, needed to determine the accurate criteria for the correction burn. We are presently doing the analysis to identify simply how much more correction of Webbs trajectory will be needed, and how much fuel will be left, however we already know that the Ariane 5s placement of Webb was better than requirements.
One fascinating aspect of the Webb launch and the Mid-Course Corrections is that we always “aim a little bit low.” The L2 point and Webbs loose orbit around it are only semi-stable. In the radial direction (along the Sun-Earth line), there is a stability point where in concept it would take no thrust to remain in position; however, that point is not stable. If Webb drifted a little bit towards Earth, it would continue (in the absence of restorative thrust) to drift ever better; if it drifted a bit away from Earth, it would continue to drift further away. Webb has thrusters just on the warm, Sun-facing side of the observatory. We would not want the hot thrusters to contaminate the cold side of the observatory with unwanted heat or with rocket exhaust that could condense on the cold optics. This means the thrusters can just push Webb far from the Sun, not back toward the Sun (and Earth). We thus create the launch insertion and the MCCs to constantly keep us on the uphill side of the gravitational capacity, we never ever want to review the crest– and wander away downhill on the other side, with no capability to come back.
For that reason, the Ariane 5 launch insertion was intentionally developed to leave some speed in the anti-Sun instructions to be provided by the payload. MCC-1a likewise was executed to secure most, however not all, of the overall required correction (to be sure that this burn also would not overshoot). In the very same way, MCC-1b, arranged for 2.5 days after launch, and MCC-2, arranged for about 29 days after launch (but neither time-critical), and the station-keeping burns throughout the mission life time will always thrust just enough to leave us a little bit shy of the crest. We desire Sisyphus to keep rolling this rock up the mild slope near the top of the hill– we never want it to roll over the crest and escape him. The Webb groups job, guided by the Flight Dynamics Facility at NASA Goddard, is to make certain it doesnt.
– Randy Kimble, JWST Integration, Test, and Commissioning Project Scientist, NASA Goddard Space Flight Center
Webbs orbit is around L2– a point of gravitational balance on the other side of Earth from the Sun– however it does not live exactly at the L2 point. At that point, Earths shadowing of the Sun would be large enough to considerably minimize the amount of power offered for Webbs solar varieties, without significantly simplifying the cooling obstacles. In addition, when Webbs interaction antennas point at Earth to receive commands, they would be blinded by the big radio emission of the Sun in the same direction. We are presently doing the analysis to identify just how much more correction of Webbs trajectory will be required, and how much fuel will be left, but we currently understand that the Ariane 5s placement of Webb was better than requirements.
The L2 point and Webbs loose orbit around it are only semi-stable.
