SDO is on Station

The third Trim Motor Firing (TMF #3) was successfully completed Tuesday evening. This apogee burn raised our perigee to geosynchronous with an orbital period of one day.

SDO is on station, next is to start up the instruments!

Tracking SDO's Attitude with the Stars

How does SDO know where it is pointing? Seems easy, just point at the brightest object in the sky! But what about our roll angle around the Sun, or where is the Sun's North Pole? SDO uses star trackers to measure its attitude. CCD images (like this one) are compared to a library to see where the star tracker is pointed. Once we know where the star trackers point we can figure out our roll angle on the Sun.

TMF-2 Complete, On to TMF-3 and Final Orbit!

Trim Motor Firing #2 was successfully completed this morning. This was different from our previous burns in being a perigee burn to raise apogee. The final orbit trim maneuver, TMF-3, is scheduled for Tuesday evening. It will be an apogee burn to raise perigee to geosynchronous and our period to one day per orbit.

SDO will see a lunar transit (the moon passing between the Sun and SDO) tomorrow morning starting at 7:22 am EDT. It will last over 3.5 hours but will not be seen on the Earth.

TMF #1 Completed, Perigee Now 35.3 Mm

The first Trim Motor Firing (TMF #1) was successfully completed Thursday evening. This apogee burn raised our perigee to 35,300 km, an orbital period of 23.6 hr. This means we are drifting 6 degrees to the east in every orbit. Two more thruster burns will be done, TMF #2 is a perigee burn to raise the apogee to its final value and TMF #3 is an apogee burn to raise the perigee to its final value. Our eastward drift will also be stopped and we will orbit the Earth once per day at the longitude of New Mexico.

Main Engine Plumbing is Vented

Tuesday night the main engine fuel and oxidizer lines were vented. SDO will now fly on thrusters for orbit station keeping and momentum control. Many thanks to the SDO propulsion team for building SDO's bi-prop system, the first to be designed and built at Goddard. Our next orbital maneuver (TMF #1) is scheduled for Thursday evening.

AMF-8 Moves SDO Perigee Altitude to 34.6 Mm

Apogee Motor Firing #8, the last orbit raising maneuver, was successfully completed Monday night. This burn raised the SDO perigee altitude to about 34,600 km for a period of about 23 hr. With this orbit SDO will appear to drift eastward toward our final longitude.

Now that we are close to our final orbit the main engine plumbing will be vented to exhaust fuel and oxidizer from the lines. The first Trim Motor Firing (TMF #1) is planned for Thursday evening.

A Successful AMF-7 Burn!

A successful Apogee Motor Firing #7 continued the string of smooth Main Engine burns since we removed the structural filter and lengthened the settling burn. AMF-7 raised our perigee altitude to approximately 25000 km, giving SDO an orbital period of about 19.2 hours. This sets SDO for one last trip "around the world" before Monday's AMF-8 actually moves SDO into a nearly geosynchronous orbit. After AMF-8, there will be three additional Trim Motor Firings (TMFs) to fix our operational orbit over White Sands.

Our Orbit so Far

Here is the SDO orbit so far. The initial GTO, two intermediate orbits, and the estimated final orbit are shown to scale. Apogee Motor Firings (AMFs) all take place at the apogee of the orbit (the left side of the diagram) and are designed to lift the perigee (where SDO is closest to the Earth) up to a geosynchronous altitude. A few trim maneuvers will then move SDO into its final orbit. Perigee values are altitudes (height above the Earth).

AMF-6 Main Engine Burn Raises Perigee Altitude to 20 Mm

Apogee Motor Firing #6 was successfully completed Tuesday evening. The burn used about 6 minutes of ACS thruster firing and 13 minutes of Main Engine firing. This maneuver raised the SDO perigee altitude to about 20,100 km, or a period of 17.4 hr. The GNC team reported that the Main Engine burn was extremely quiet and the momentum disturbance due to the fuel sloshing was minimal. Due to the equipment outage at the Santiago ground station, most of ranging this evening was performed by SDOGS.

AMF-5, A Combined Thrusters and Main Engine Burn, Raises Perigee Above 15 Mm

Apogee Motor Firing #5 used the ACS thrusters and main engine to raise the perigee altitude of SDO to about 15,000 km on the way to our target of 35,800 km. (Using Kepler's law, my estimate of the current orbital period is about 15.4 hr.) We had a very smooth burn so we will use the main engine for the next burn that is scheduled for Tuesday evening.

Thanks to the slosh tiger team for their hard work on redesigning the flight software!