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From this answer to my previous DSCOVR question, and this and this and this article, it seems that DSCOVR used one or more of its ten thrusters for the long burns for mid course correction (MCC) and Lissajous orbit insertion (LOI). These were to be 50 minutes and 5.3 hours, respectively.

How did the spacecraft maintain the proper thrust direction? If it were a single engine located on a central axis, it might have been slightly gimbaled. But for these 5N thrusters, were they distributed around an axis and used in groups of 3 or more? During a long burn, it's important to maintain the thrust vector in the correct direction. Were they pulsed in order to maintain the proper direction, or other thrusters on the sides used, or attitude adjusted with reaction wheels (gimbaling the entire spacecraft)?

I would also like to see a drawing of some kind indicating the locations of the ten thrusters and the directions they point, so I can visualize this better.

note: "They could have..." type answers are sometimes helpful, but here I'd like something definitive.

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The report 'Resurrected DSCOVR Propulsion System – Challenges and Lessons Learned' contains a schematic of the propulsion system:

DSCOVR thrusters schematic diagram. Thrusters 1-8 are installed in pairs, 9 and 10 are axial thrusters.

and indicates thruster locations:

DSCOVR is a cylinder, thruster 1-8 are installed around the sides of the cylinder, 9-10 are on the bottom.

thruster 9 and 10 are on the bottom:

more locations

The thrusters were used as follows:

... the DSCOVR propulsion system, which utilizes ten 4.5 N thrusters in blowdown mode to perform Midcourse Correction (MCC) maneuvers, Lissajous Orbit Insertion (LOI) at Lagrangian point L1, momentum unloading maneuvers, and station keeping delta-v maneuvers at L1.

The first planned thruster maneuver was the MCC burn, which was designed to correct any launch dispersion in the spacecraft trajectory. ... The MCC #1 maneuver was actually performed using Thrusters 9 and 10 for +Z delta-V direction and Thrusters 1 through 8 for attitude control.

On June 7, 2015 (115 days after launch), the Lissajous Orbit Insertion (LOI) burn placed DSCOVR in orbit at the Sun-Earth L1 Lagrangian point. The burn consisted of two segments: one burn approximately 4 hours long (152.4 m/s) and a second burn approximately 35 minutes long (13.9 m/s). The burn was performed in two segments so the Flight Dynamics team could re-calibrate the second segment based on the information from the first segment. The thruster configuration used Thrusters 9 and 10 for +Z delta-V and the Thrusters 1 through 8 as needed for attitude control.

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  • $\begingroup$ Excellent! Thank you for tracking this down. For some reason I never actually noticed the propulsion module in the photos, for example here, here, and here - but now it's obvious! I wonder if that white collar at the bottom supports the satellite and attaches to 2nd stage while protecting the Axial Thrusters? $\endgroup$ – uhoh Mar 1 '16 at 14:14

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