Answers Your Questions
| From: Bill Luhn, of Chicago,
To: John Curry, flight director
Question: Since the shuttle is moving faster than the ISS until it catches up to it, physics would dictate that it must also be in a higher orbit. How much higher is the shuttle's orbit than the ISS' while it is catching up?
Answer: Actually, the shuttle must be in a lower orbit than ISS in order to travel faster and catch up. The ISS altitude is approximately 210 nautical miles (nm). The shuttle initially launches into a 122 x 85 nm orbit and immediately begins a series of burns that by the second flight day places it in a catch-up orbit of roughly 190 x 170 nm (for STS-113). By the next day, rendezvous day, further burns have raised the orbit to about 210 x 180 nm (note that the high point, or apogee, now matches the ISS orbit). On rendezvous day, a series of finer burns culminates in the shuttle meeting up with and matching the orbit of the station, at which point the two vehicles dock.