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SpaceX Successfully Completes First Mission to Geostationary Transfer Orbit

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Re: SpaceX Successfully Completes First Mission to Geostationary Transfer Orbit

#21

Post by cecilpl »

Tuna-Fish wrote: post #20
some_guy_there wrote: post #5

Can anyone explain why they placed the satellite in 295x80 000 km orbit? Is it especially hard to place satellites directly into geostationary orbit, or something else?

The reason they temporarily raise their apogee so high is that it reduces the delta-v cost of changing inclination. The cost of changing inclination is directly proportional to your speed at the moment when you do the inclination change. When you are in a highly eccentric orbit, your speed at apoapsis is much lower than your speed in a circular orbit. Also, inclination burns can be combined with raising periapsis, wh…

> If this is interesting, and you don't already own kerbal space program, head over to the steam store right now.

And if you like Kerbal Space Program, but you find it isn't quite sadistic enough, go download Orbiter.

Re: SpaceX Successfully Completes First Mission to Geostationary Transfer Orbit

#22

Post by everyone »

I dont like spaceXs propoganda department. I believe this is a difference between a public and a private space program. SpaceX seem to cover up any hiccups or issues they have and always present this saccharine sweet 'flawless' report of their missions. Thats dishonest and just not scientific imo.

Re: SpaceX Successfully Completes First Mission to Geostationary Transfer Orbit

#23

Post by InclinedPlane »

everyone wrote: post #22

I dont like spaceXs propoganda department. I believe this is a difference between a public and a private space program. SpaceX seem to cover up any hiccups or issues they have and always present this saccharine sweet 'flawless' report of their missions. Thats dishonest and just not scientific imo.

They seem to be incredibly open to me. They have been very transparent about pretty much every hiccup and misstep they've had in any flight. I think you are comparing them to an ideal which has never existed in reality.

Re: SpaceX Successfully Completes First Mission to Geostationary Transfer Orbit

#24

Post by pjscott »

everyone wrote: post #22

I dont like spaceXs propoganda department. I believe this is a difference between a public and a private space program. SpaceX seem to cover up any hiccups or issues they have and always present this saccharine sweet 'flawless' report of their missions. Thats dishonest and just not scientific imo.

A few entries from Elon Musk's Twitter feed, from the first launch attempt a couple days ago:

> Launch aborted by autosequence due to slower than expected thrust ramp. Seems ok on closer inspection. Cycling countdown.

> Increasing helium spin start pressure. Probably > We called manual abort. Better to be paranoid and wrong. Bringing rocket down to borescope engines ...

> All known rocket anomalies resolved. Will spend another day rechecking to be sure. Launch attempt tmrw eve w Wed as backup.

Press releases are press releases, and a press release will always spin things as favorably as possible. If you look at the other sources, though, they seem awfully forthright.

Re: SpaceX Successfully Completes First Mission to Geostationary Transfer Orbit

#25

Post by everyone »

InclinedPlane wrote: post #23
everyone wrote: post #22

I dont like spaceXs propoganda department. I believe this is a difference between a public and a private space program. SpaceX seem to cover up any hiccups or issues they have and always present this saccharine sweet 'flawless' report of their missions. Thats dishonest and just not scientific imo.

They seem to be incredibly open to me. They have been very transparent about pretty much every hiccup and misstep they've had in any flight. I think you are comparing them to an ideal which has never existed in reality.

They cut the live feed when an issue came up on one of their dragon capsule launches.

Re: SpaceX Successfully Completes First Mission to Geostationary Transfer Orbit

#26

Post by exDM69 »

JshWright wrote: post #15
ubernostrum wrote: post #11

Earlier quoted context omitted.

So, orbits are weird. As in, "burning your engines in space almost never does what you'd intuitively expect based on a lifetime on Earth with things like cars and planes" weird. In order to get geostationary, you need to get to a circular orbit at an altitude of 35,786km above Earth's surface. Trying to do that all in one burn is, I guess, theoretically possible but is going to waste an absurd amount of fuel. The rea…

This is made even more complicated by the fact that SpaceX isn't launching from the equator, which means the satellite will need to change its orbital inclination. Inclination changes are less expensive the 'higher' up you are, so SES8 is in an orbit with an apogee almost twice as high as its eventual orbit. This allows it to use less fuel to correct the inclination. I haven't read up on the burn plans, but it's poss…

Bi-elliptic transfer sounds like a plausible explanation but my math gives it a bigger delta-v requirement than a straightforward Hohmann transfer.

Bi-elliptic transfer: (2.713240 + 0.908982 + 0.485255) = 4.107477 km/s Hohmann transfer: (2.335977 + 1.431307) = 3.7672853 km/s

This alone does not explain why they did so. But this is all assuming that the trajectory is planar. If there was a plane change coupled with the second burn at high apogee, it could explain it.

Re: SpaceX Successfully Completes First Mission to Geostationary Transfer Orbit

#27

Post by zackbloom »

everyone wrote: post #25
InclinedPlane wrote: post #23

Earlier quoted context omitted.

They seem to be incredibly open to me. They have been very transparent about pretty much every hiccup and misstep they've had in any flight. I think you are comparing them to an ideal which has never existed in reality.

They cut the live feed when an issue came up on one of their dragon capsule launches.

You don't think NASA wouldn't have cut the feed on the Challenger disaster if they could have?

Re: SpaceX Successfully Completes First Mission to Geostationary Transfer Orbit

#28

Post by ghshephard »

everyone wrote: post #25
InclinedPlane wrote: post #23

Earlier quoted context omitted.

They seem to be incredibly open to me. They have been very transparent about pretty much every hiccup and misstep they've had in any flight. I think you are comparing them to an ideal which has never existed in reality.

They cut the live feed when an issue came up on one of their dragon capsule launches.

There is a little bit of hyperbole involved when you have an issue with them cutting the live feed on one of their missions and then claiming:

"SpaceX seem to cover up any hiccups or issues they have and always present this saccharine sweet 'flawless' report of their missions. "

You may want to dial it back a few notches - trust me, I tend to reach for the hyperbole a little too quickly myself.

(Note - I read subscribe to Elon Musk's twitter feed, and he's a lot more balanced on SpaceX than he is on Tesla)

Re: SpaceX Successfully Completes First Mission to Geostationary Transfer Orbit

#29

Post by rplnt »

zackbloom wrote: post #27
everyone wrote: post #25

Earlier quoted context omitted.

They cut the live feed when an issue came up on one of their dragon capsule launches.

You don't think NASA wouldn't have cut the feed on the Challenger disaster if they could have?

Perhaps, but there were people on Challenger. Not that it would look any different on cameras...

Re: SpaceX Successfully Completes First Mission to Geostationary Transfer Orbit

#30

Post by rplnt »

InclinedPlane wrote: post #23
everyone wrote: post #22

I dont like spaceXs propoganda department. I believe this is a difference between a public and a private space program. SpaceX seem to cover up any hiccups or issues they have and always present this saccharine sweet 'flawless' report of their missions. Thats dishonest and just not scientific imo.

They seem to be incredibly open to me. They have been very transparent about pretty much every hiccup and misstep they've had in any flight. I think you are comparing them to an ideal which has never existed in reality.

IIRC they weren't exactly open about losing a satellite in a ISS resupply mission[1].

1. http://en.wikipedia.org/wiki/SpaceX_CRS-1#Secondary_payload

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