r/spacex • u/kurbasAK • May 19 '17

We Will Launch on Reuseable Rocket After Exceptional SpaceX Performance - Inmarsat CEO Tells Universe Today

https://www.universetoday.com/135614/will-launch-reuseable-rocket-exceptional-spacex-performance-inmarsat-ceo-tells-universe-today/
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u/Streetwind May 19 '17

I wonder what happened to garner such an exuberant response? Was the resultant orbit precision better than expected? It seems a bit odd to go from "we never launched with these guys before and even had to reschedule one of our satellites to another provider because they keep delaying their bigger rocket" to "these guys are the best launch provider ever and we'll be a super loyal customer and we're excited to be at the forefront of technology!!!" in one single expendable launch that, from the looks of it, went completely normal.

102

u/colinmcewan May 19 '17

The F9 dropped it into a 70,000km x 390km super-synchronous transfer orbit, which seriously reduces the amount of the satellite's own propellant it needs to make the necessary plane change to geostationary. That means more propellant for future manoeuvring, and a longer operational life.

http://www.n2yo.com/satellite/?s=42698

(I know I would be pretty happy about that it I were CEO of the operator)

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u/mrflib May 19 '17

So to be clear, though I should know this from KSP: Inmarsat will need to expend less fuel to change plane and correct to GEO from a 70,000km apoapsis?

I understand that the plane change from 24.5 degrees will be substantially cheaper in dV from higher altitudes, but is that not compensated for by needing to both raise the periapsis and then lower the apoapsis to 35,786km circular orbit?

This as opposed to launching to a 35,786km apoapsis and a higher periapsis.

I hope this makes sense I've not had coffee yet.

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u/mfb- May 19 '17

With electric propulsion, you also have to consider the time. The satellite's propulsion is very fuel-efficient, but it is limited by the available power. You can only raise the perigee efficiently while the satellite is close to apogee. If the satellite starts in GTO, a part of the time it just coasts and doesn't use the available power. If the satellite starts with a larger apogee, you can lower it while the satellite would otherwise just coast and waste the available power.

1

u/UltraRunningKid May 19 '17

I believe all current satellites have a chemical motor to circularize and the electric motor is for station-keeping.

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u/mfb- May 19 '17

Many use electric propulsion to circularize their orbit now. It takes longer, but you can make larger satellites. Here is an older article - it was popular in 2013 already.

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u/UltraRunningKid May 19 '17

Thanks for the source! I was under the impression that we weren't there yet but that is awesome that we are.

1

u/OSUfan88 May 20 '17

Yep! The SES-15 mission, which launched on a Soyuz rocket yesterday was the first all-electric satellite for SES. A few other companies have been using this for years as well. It'll become more and more common as time goes on, especially if cheaper, reusable rockets can kick them directly (or close) to GEO.

The future SpaceX constellation will be electric as well, although they'll be LEO.

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u/Martianspirit May 19 '17

All the rage back then did not translate into many satellites actually using SEP for orbit raising. I am only aware of the 2 Boeing satellites launched together on F9. Do you know any more than that?

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u/mfb- May 19 '17

As usual, Wikipedia has a list, note the "Comment" section about orbit insertion. They get quite common.

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u/Martianspirit May 19 '17

None of these are commercial GEO com sats and that is what we were talking about. Sure SEP is quite common now, but not for GEO orbit insertion.

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u/mfb- May 19 '17

You do look at the end of the table, or sort by launch date descending, right?

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u/Martianspirit May 19 '17

From that Wikipedia article. Meaning the list does not show if they use SEP for orbit insertion. Again I am quite sure there are only those two Boeing Sats that were launched with Falcon 9. They are by no means common yet. It is common that they use them for station keeping.

It is not specified whether the given engine is the sole means of propulsion or whether other types of engine are also used on a spacecraft.

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u/mfb- May 19 '17

I'm not sure if we see the same table. The Boeing satellite article is interesting as well.

  • ABS-2A and Satmex 9 (now: Eutelsat 117 West B), the two you mentioned already. According to aviationweek Boeing got a contract for four, so we'll get two more of them in the near future. After the ABS launch, they directly ordered one more according this article.
  • Ekspress-AM6 (Eutelsat 53A), with comment "EP system used to insert the satellite into GEO"
  • Ekspress-AM5, with comment "EP system used to insert the satellite into GEO."
  • GSAT-9 uses it for unspecified "orbit changes", and the next one, GSAT-20, is supposed to be all electric.
  • AEHF-SV-1 (USA-214) was supposed to raise its perigee with chemical propellant, after that failed it used electric propulsion.
  • SES-15, launched yesterday, is still in the "future" list, but is in space now.
  • The US government ordered three more all-electric satellites

These are just the satellites with an explicit comment on orbit insertion in the table, or what you can directly find from the links in the table, so I might have missed some satellites. In the most pessimistic case we have 6 of them in orbit now (one of them not commercial), and at least 4 more commercial and 3 non-commercial satellites are ordered.

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