SkySat-3, launched in June 2016 on PSLV, was the first commercial spacecraft to load and fly ECAPS' ADN based green monopropellant known as LMP-103S. Previously the technology had flown on the Swedish Space Corporations PRISMA mission, which launched in June 2010.
Evolution of SkySat
In November 2013 Skybox Imaging launched SkySat-1 from Yasny, Russia. Eight months later SkySat-2 was launched from Baikonur, Kazakhstan. Shortly afterward Skybox Imaging was aquired by Google and rebranded to Terra Bella. To enhance mission flexibility and increase on-orbit life, the next design iteration of the SkySat platform incorporated a chemical propulsion subsystem.
Need for Propulsion
A critical requirement identified in the evolution from SkySat-1 and SkySat-2 towards a full constellation (SkySat-3 thru SkySat-21) was the inclusion of a highly performant propulsion system capable of maximizing available within a tight volume and low power restrictions. The chief capabilities enabled by inclusion of such a propulsion system are:
- Constellation Phase Management
- Launching multiple spacecraft on a single rocket requires the use of propulsion to phase the spacecraft within each orbit plane and then overcome orbit perturbations to maintain their relative spacing
- Mission Flexibility
- A high thrust to spacecraft mass propulsion system enables the constellation to take advantage of a wide range of primary or secondary launch opportunities with established providers and emerging new entrants. The ability to correct for large orbit injection errors or accept injection into a wide range of altitudes and quickly absorb those individual launch differences without significant delay to incorporation of spacecraft into the constellation’s product is a tremendous value
ECAPS System Used on SkySat-3 to SkySat-21
The resulting system was designed and manufactured by ECAPS AB in Solna, Sweden. It is a fully integrated, modular drop-in to the existing SkySat bus design, which was extended in height to include the propulsion system.
The system provides a total impulse of approximately 21 kN-s at a satellite internal volume fraction of about 11% and a mass fraction of approximately 10% dry and 19% wet. Four 1N HPGP thrusters are blowdown pressure fed LMP-103S from 3 tanks holding 10.5 kg of propellent total. The schematic and physical layout is shown in Figure 1.
Cumulative Time in Space
At the time of posting, SkySat-3 to SkySat-15 are operating in-space and SkySat-16 to SkySat-21 are scheduled to be launched in summer of 2020 on SpaceX Falcon 9 vehicles (SkySat-1 and 2 are excluded because they do not have propulsion systems). The total on-orbit years for the ECAPS propulsion systems are tabulated below:
|Satellites||Vehicle||Site||Date||Sat Years In Space|
|SkySat-3||PSLV||Sriharikota, India||June 2016||3.9|
|SkySat-4, 5, 6, 7||Vega||Kourou, French Guiana||Sept 2016||14.9|
|SkySat-8, 9, 10, 11, 12, 13||Minotaur||Vandenberg, USA||Oct 2017||15.5|
|SkySat-14, 15||Falcon 9||Vandenberg, USA||Dec 2018||3.0|
For more detailed information and on-orbit operation results, take a look at these conference papers:
"On-Orbit Operation and Performance of Ammonium Dinitramide (ADN) Based High Performance Green Propulsion (HPGP) Systems", Peter Friedhoff, Alisa Hawkins, John Carrico, Jonathan Dyer, Kjell Anflo, 2017 Joint Propulsion Conference. July 2017
"Growing Constellation of Ammonium Dinitramide (ADN) Based High Performance Green Propulsion (HPGP) Systems", Peter Friedhoff, Kjell Anflo, Peter Thormahlen, Mathias Persson. 2018 Joint Propulsion Conference. July 2018