T oday's launch window is an "instantaneous" one - meaning the rocket has to lift off at exactly 4.33pm or we have to try again on Saturday. Why would a mission to Sun-Earth L1 have an instantaneous launch window? But why did we need a launch window for Mars Express? With less than hour before launch at 10:21 a.m. EDT, the countdown continues on schedule.
The most significant deciding factors in when to launch are where the spacecraft is headed, and what its solar needs are.
Imagine the Solar System as an athletics race track. Ultimately, the launch window and preferred liftoff time are set by the launch service contractor. That means the launch window is 1-second today, otherwise the launch … Achieving the correct orbit requires the Right Ascension of the Ascending Node (RAAN).
RAAN is set by varying a launch time, waiting for the earth to rotate until it is in the correct position. For missions with very specific orbits, like rendezvousing with the International Space Station the launch window may be a single moment in time, known as an instantaneous launch window. SpaceX is standing down from today's launch of its tenth Starlink mission due to weather conditions. The Mars Express launch window had opened on 23 May and would last for four weeks. The SpaceX teams are working with the Range to determine the next available opportunity for launch of 57 Starlink satellites and 2 BlackSky satellites, a Spaceflight customer, from Launch Complex 39A (LC-39A) at Kennedy Space Center in Florida. The SpaceX Falcon 9 and Dragon spacecraft are timed precisely to lift off at the optimum point to reach the space station, which is zooming overhead 249 miles above Earth at 17,500 mph. "We help everybody understand the requirements of the spacecraft and what the capabilities are of the launch vehicle, and try to mesh the two," Haddox explained. Falcon 9 does actually have about a 5 minute launch window on either side to get Dragon to orbit so it can get to the ISS, but because terminal count begins at T-10 minutes or so, and any scrub or hold inside terminal count requires a restart from T-10 minutes (at least), they only get a single shot to launch it, so the window is effectively instantaneous. In fact, liftoff can't wait even 1 second — what's called an "instantaneous" launch window — because of the rocket's design and the trajectory of the ISS over Earth.
8:34PM Space Station gives the OK
Launch Window Instantaneous Today. If we are going to send a mission to a planet, why not just launch the rocket at any time, find where Mars is in the sky, point the rocket at it and travel there?