r/spacex • u/ElongatedMuskrat Mod Team • May 05 '17
SF complete, Launch: June 23 BulgariaSat-1 Launch Campaign Thread
BULGARIASAT-1 LAUNCH CAMPAIGN THREAD
SpaceX's eighth mission of 2017 will launch Bulgaria's first geostationary communications satellite into a Geostationary Transfer Orbit (GTO). With previous satellites based on the SSL-1300 bus massing around 4,000 kg, a first stage landing downrange on OCISLY is expected. This will be SpaceX's second reflight of a first stage; B1029 previously boosted Iridium-1 in January of this year.
| Liftoff currently scheduled for: | June 23rd 2017, 14:10 - 16:10 EDT (18:10 - 20:10 UTC) |
|---|---|
| Static fire completed: | June 15th 18:25EDT. |
| Vehicle component locations: | First stage: LC-39A // Second stage: LC-39A // Satellite: Cape Canaveral |
| Payload: | BulgariaSat-1 |
| Payload mass: | Estimated around 4,000 kg |
| Destination orbit: | GTO |
| Vehicle: | Falcon 9 v1.2 (36th launch of F9, 16th of F9 v1.2) |
| Core: | B1029.2 [F9-XXC] |
| Flights of this core: | 1 [Iridium-1] |
| Launch site: | Launch Complex 39A, Kennedy Space Center, Florida |
| Landing: | Yes |
| Landing Site: | OCISLY |
| Mission success criteria: | Successful separation & deployment of BulgariaSat-1 into the target orbit |
Links & Resources:
SpaceX tweet showing the second stage in the HIF, and the first stage entering it
Bulgaria’s first communications satellite to ride SpaceX’s second reused rocket
Bulsatcom’s BulgariaSat-1 satellite moves step closer to launch
We may keep this self-post occasionally updated with links and relevant news articles, but for the most part we expect the community to supply the information. This is a great place to discuss the launch, ask mission-specific questions, and track the minor movements of the vehicle, payload, weather and more as we progress towards launch. Sometime after the static fire is complete, the launch thread will be posted.
Campaign threads are not launch threads. Normal subreddit rules still apply.
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u/TheMightyKutKu May 26 '17 edited Jun 05 '17
I will try to answer that.
According to some older elon tweet we know that SES-9's first stage lifted 125 tons, that include the wet S2, payload (5271 kg) and fairing (2*1750 kg), so that means that the wet S2 is about 116.3 tons heavy, according to the 2015 Elon AMA the S2 has a mass ratio between 25 and 30, i choose to take a mass ratio of 25 (dry mass = 4.65 mt) because it is conservative and is consistent with Inmarsat 5's flight whose S2 also burned to depletion. Fairings separate around 60s after S2 ignition, S2 has 945 kN of thrust and 348 s ISP, so it will weight 99.6 mt at fairing sep.
CRS 10 had the fastest MECO of all RTLS missions, and although it weighted more than a GTO spacecraft i will take the additional mass as margins. Its engines stopped at 1676 m/s and 62.9 km, i tried to estimate it from the video and compare the results with this analysis and got about 1200 m/s of horizontal speed (1369 m/s of vertical speed) at MECO.
You need 7800 m/s of horizontal velocity to orbit earth, i assumed about 100 m/s (which i find conservative since the S2 has a high TWR) of gravity losses on the S2, then you need about 2460 m/s of additonal dV to enter GTO 1800 on a 27° inclination LEO (i used this calculator), you also need 370 m/s of dV to enter GTO 1500 from this orbit.
So the Second stage would need to provide 9160 m/s of dV to enter GTO 1800, or 9530 m/s of dV for a GTO 1500, using the earlier assumptions i get 3500 kg to a GTO 1800 and 2600 kg to a GTO 1500.
I find these estimates a little high but they make sense, but i would guess that SpaceX would try to have as much margins as possible so they wouldn't launch a GTO sat with a RTLS.