SpaceX will launch it's first geo satellite Tue 3rd Dec

[K^2]

No, the LEO to GTO burn is about 2.5km/s. GEO to LTO is, indeed, about 3.1km/s.

For sake of completion, GTO to GEO is another 1.5km/s. Could you have been thinking of total LEO to GEO, which is about 3.9km/s?

Edited December 4, 2013 by K^2

[ferram4]

No, that doesn't sound right. Assuming a 200 km circular orbit, the vehicle's velocity is:

v_circ = sqrt(mu_Earth / r)

v_circ = sqrt[398,600 km³s^-2 / (200 km + 6,378 km)]

v_circ = 7.784 km/s

Then, a GTO from 200km would have a semimajor axis of:

a = (r_ap + r_pe) / 2

a = [(6,378 km + 35,768 km) + (200 km + 6,378 km)] / 2

a = 24,362 km

And then the velocity at periapsis would be:

v_pe = sqrt[mu_Earth * (2 / r_pe - 1 / a)]

v_pe = sqrt[398,600 km³s-2 * (2 / (200 km + 6378 km) - 1 / 24,362 km)]

v_pe = 10.239 km/s

dV = v_pe - v_circ

dV = 2.459 km/s

Hunh. I thought that GTOs were more elliptical and closer to the point where tiny amounts of dV resulted in huge changes in apoapsis. Whoops. I'm wrong.

[SFJackBauer]

@ Camacha: no, I meant what's the delta-v for the apogee raising burn, not for the circularization one.

Assuming the parking orbit was at 295km, and since its final apogee was 80,000km, the burn to reach this apogee would be 2804 m/s.

After that, once the satellite reaches apogee, it will burn simultaneously radially and prograde to both reduce its inclination, and raise the perigee from 295km to 35,786km (I don't know if it will do a single burn or several burns over several orbits).

Then, once its perigee has been raised to 35,786km, it will burn retrograde at perigee to reduce its apogee from 80,000km to 35,786km, which will consume 490 m/s of deltaV.

Basically this pic:

Edited December 4, 2013 by SFJackBauer

[SFJackBauer]

Also, it could also be done this way:

- Burn at perigee (295km) to raise apogee to 80,000km

- Burn radially at apogee to reduce inclination

- Burn at perigee to reduce apogee to 35,786km

- Burn at apogee to raise perigee to 35,786km

Which approach is cheaper?

Edited December 4, 2013 by SFJackBauer

[K^2]

Bi-elliptic is 2,802 + 926 + 490 = 4,218m/s.

Alternative: 2,802 + 375 + 1,467 = 4,644m/s.

Neither of these include inclination change burn, but that's going to be identical, making bi-elliptic transfer significantly cheaper.

Do you know how much inclination change is required? I want to see how much bi-elliptic saves compared to doing inclination change in LEO.

[The Destroyer]

Boy, it took awhile to launch! Hope they learn and improve things for future launches- on a Mars mission, timing could be crucial...

[Albert VDS]

It's better to have smaller problems every launch than, for example, having 9 smooth launches and the 10th being a fireball.

Edit: For anyone who missed it, here's a youtube video of the webcast:

Edited December 4, 2013 by Albert VDS

[Kilmeister]

Thanks for the link, I was about to come here and ask for one.

[Meithan]

Bi-elliptic is 2,802 + 926 + 490 = 4,218m/s.

Alternative: 2,802 + 375 + 1,467 = 4,644m/s.

Neither of these include inclination change burn, but that's going to be identical, making bi-elliptic transfer significantly cheaper.

Do you know how much inclination change is required? I want to see how much bi-elliptic saves compared to doing inclination change in LEO.

Well, Cape Canaveral Air Force Station is at latitude 28.5°, so that's the minimum orbital inclination if you launched "straight". I think it's a good estimate of the inclination change required.

Edit: also, this was reported on spaceflight101:

The second stage ignited after passing the T+27-minute mark and completed a burn of about 71 seconds to boost the apogee of the orbit to 80,000 Kilometers and reduce the inclination of the orbit from 28 to 20.75 degrees. This Supersynchronous Transfer Orbit allows SES-8 to perform an energy efficient transfer into Geostationary Orbit requiring a total change in velocity of 1,500 meters per second as opposed to 1,800m/s for a standard GEO Transfer Orbit. SES-8 was detected in a 385 by 79,129-Kilometer orbit at an inclination of 20.5°.

Edit 2: more details:

Target Orbit: 295 by 80,000km, 20.75°

Achieved Orbit: 385 by 79,129km, 20.54°

Edited December 4, 2013 by Meithan

[K^2]

Yeah, that's definitely everything I would need. So we have 3 burns in planned bi-elliptic.

295 by 295 at 28.5° to 295 by 80k at 20.75°

295 by 80k at 20.75° to 35,786 by 80k at 0°

35,786 by 80k at 0° to 35,786 by 35,786 at 0°

I'll run these.

[Meithan]

But I'd calculate the delta-v requirements for the part of the journey carried out by the payload, SES-8 in this case.

That is, I'd compare two options:

Option A: launch rocket puts payload into standard GTO with a 36,000 km apogee. Payload then performs a circularization and inclination change burn at apogee.

Option B: launch rocket puts payload into supersynchronous GTO, with the apogee at 80,000 km. Payload performs an inclination change and periapsis raise (to GEO altitude) burn at apogee. Then, at perigee, payload performs a circularization burn (the standard bielliptic).

Also one has to keep in mind that burns can combine simultaneously change in periapsis/apoapsis and inclination, and that it's cheaper than doing separate burns. But I think SES-8 is scheduled to do something like 5 burns in order to reach final GEO.

[K^2]

can combine simultaneously change in periapsis/apoapsis and inclination

Of course. That's the way I would compute the above.

[Meithan]

I just had to sit an exam, and in order to kill time I did the calculations on a sheet of paper.

Assuming that the payload is injected into a standard GTO (385 by 35,780 km, 20.5°), it requires about 1660 m/s to do the combined inclination change + circularization at apogee. This is less than the 1800 m/s mentioned above, so I might be wrong here.

If, instead, the payload is initially injected into a supersynchronous 385 x 80,000 km, 20.5° orbit, it requires about 1014 m/s to do the combined inclination change + periapsis raise at apogee, and then 491 m/s for the circularization. That's a total of 1505 m/s. While it's still cheaper, the difference is not that large, but I suspect I made a mistake in the first calculation. Will recheck.

[Kryten]

We now have some quite good footage of staging and fairing separation from the ground.

[Albert VDS]

That was too hilarious!

[Sun]

I MISSED IT! *facepalm x3,000,000,000,000*

[PakledHostage]

We now have some quite good footage of staging and fairing separation from the ground.

I figure their conversation is about analagous to many of our own conversations on this forum. Everybody has an opinion and almost nobody knows what they are talking about.

Edited December 5, 2013 by PakledHostage

[nhnifong]

Breaking news: SpaceX Launched a meteor.

[Tommygun]

I figure their conversation is about analagous to many of our own conversations on this forum. Everybody has an opinion and almost nobody knows what they are talking about.

But the Mom knew.

[Scotius]

Makes you feel a tiny little bit superior...isn't it? On a more serious note - very cool video. Those folks were extremely lucky (too bad they did not know it was actually way cooler thing than mere meteor). And it made me sad - we live in XXI century, rockets are launched on monthly basis - but no one said "Hey, it's a rocket."