2
$\begingroup$

I just wrote (and have since removed) the following paragraph in this answer:

As can be heard in this video SpaceX's launch of the DSCOVR spacecraft to Sun-Earth L1 went there almost directly. The first secondary engine cut-off (SECO-1) was at about T+ 00:08:40, and after what the announcer says (at about T+ 00:09:50) would be "in about 21 minutes", the secondary stage's second burn would put it in to a Heliocentric orbit (along the stable manifold of it's future SE L1 Halo orbit) on it's way to the SE L1. Considering that a LEO orbit is about 90 minutes, DSCOVR was in Earth orbit for roughly half of one Earth orbit. (emphasis added)

DSCOVR would need about four months to arrive in its final orbit, and explained in the answers to Why would a mission to Sun-Earth L1 have an instantaneous launch window? was probably traveling along the most efficient (lowest Δv) path to arrive there.

edit: Based on comments, I should explain that my use of "probably traveling along the most efficient" comes from a reading of the paper Resurrected DSCOVR Propulsion System – Challenges and Lessons Learned that nicely describes DSCOVR's propulsion system and lists the two mid-course corrections used:

The first planned thruster maneuver was the MCC burn, which was designed to correct any launch dispersion in the spacecraft trajectory. Since the Falcon 9 trajectory resulted in a low launch dispersion, the MCC #1 burn only required a burn duration of 37 seconds (0.4895 m/s). The maneuver was performed successfully 32 hours after launch.

MCC #2 was performed on April 28, 2015, as a +Z maneuver with a burn duration of 3.1 minutes (about 2.449 m/s).

Launch was 11-Feb-2015, so MCC #2 happened at around day ~77.

  • Is the idea that DSCOVR travelled on a trajectory along a CR3BP manifold at least generally correct?

  • Is the wording at least fairly accurate, or is there a better way to say this? If I understand correctly, DSCOVR is actually in a Lissajous orbit, not technically a halo orbit, although sometimes they get lumped together. In that case is there still a manifold?

Possibly helpful items:

  1. Lissajous Orbit Control for the Deep Space Climate Observatory Sun-Earth L1 Libration Point Mission
  2. Fig. 1 of Early Mission Maneuver Operations for the Deep Space Climate Observatory Sun-Earth L1 Libration Point Mission
  3. page 3 of DSCOVR Halfway to L1

enter image description here

$\endgroup$
  • 1
    $\begingroup$ My boss is in charge of this mission and he joked that the Space-X engineers were puzzled when he (and others) initially approached them about possibly using a Falcon rocket to get to L1. He told them the C3 necessary and they laughed because they thought he was joking (apparently it's not much). Apparently the rocket had way more than enough thrust to send the payload directly to L1 (obviously not a straight line as that would be a lot of dV) so I do not think a stable manifold trajectory was necessary, but am not sure... $\endgroup$ – honeste_vivere Jan 19 '18 at 15:35
  • $\begingroup$ @honeste_vivere Since the F9 stage 2 propellants are cryogenic, they need to be used right away. They wold not be available for the following 110 days, so if there wasn't a manifold to follow, only DSCOVR's own engines would be available to navigate to its Lissajous orbit. So it's not only a function of the total delta-v, but how much is available over those four months. $\endgroup$ – uhoh Jan 19 '18 at 15:45
  • 1
    $\begingroup$ Yes, I know but what I meant was that once past basically the moons orbit the trajectory is altered in a minimal way and only small corrections are necessary. They do need to worry about stable manifolds for orbit insertion, which can often influence the cruise phase but I do not think they needed to worry much with DSCOVR until insertion at L1 (at least this is what I recall from that time). I guess my point is that the small cruise between Earth and L1 is not really the critical piece other than dV needed at insertion and staying near the ecliptic plane. $\endgroup$ – honeste_vivere Jan 19 '18 at 16:15
  • $\begingroup$ @honeste_vivere OK got it. I'm happy for any and all insight into DSCOVR's trajectory, thanks! See the edit; it looks like a Δv of only about 3 m/s was needed between separation from F9 2nd stage and orbit insertion. However, there were quite sizable insertion burns (page 12) so that may be the basis of an answer. $\endgroup$ – uhoh Jan 21 '18 at 0:24

Your Answer

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Browse other questions tagged or ask your own question.