I used to love watching shuttle launches, and they would sometimes delay missions a day or two due to weather, even if the rain/snow would be over in a few hours. Why couldn’t they just wait instead of delaying?
In: Planetary Science
A launch window implies that the vehicle needs to rendezvous with another object that is orbiting, such as a space station or the Moon. Those objects are also in motion, so you need to time the launch right to intercept their paths.
Rockets have a very limited amount of fuel which they need to maneuver in space. A launch window to join up with the ISS for instance is a frame of time that they can launch and directly into a good spot to make the join up in with the least amount of fuel and in the most efficient manner possible. Launching outside that launch window would require either too much fuel or take a lot of time to make the join up.
One possible explanation is the target they are aiming for is out of reach. Let’s say they are trying to rendezvous with craft that is already in orbit. They have a “window” of time to get there, if they miss it, then the craft in orbit may be on the opposite side of the planet when the launch vehicle gets up there.
This would require the launch craft to use additional resources to reach the craft. Additional resources means additional money needs to be spent. It would just be cheaper to wait until the window comes around again.
To meet up with something in space takes either very good timing, or a shit ton of fuel. Rockets don’t have very much (if any) extra fuel, so they have to have good timing. Imagine you’re walking to the bus stop, and you just miss it. Do you wait for the next one, or sprint at the bus and hope you catch up before you get too tired?
Rocket Science!
It’s very precise, and a launch window is calculated based on numerous factors that give the “best” window of launch to eliminate any and all possibilities of failure and mitigate as much risk as possible.
Things like wind speed, cloud formation, ambient temperature etc. all play a part in determining when the best time to launch is. The Big things though, is where is your target in relation to you.
If you want to intercept the ISS from Cape Canavral, you’re going to need to make sure to launch at a point where the ISS’s orbit is going to meet up with your launch vehicle, otherwise, you could literally end up on the wrong side of the planet from your target, and not enough fuel to make corrective maneuvers to reach your destination.
Everything going into space has to be measured to conserve as much fuel as physically possible and to reach the correct orbit, going the right speed, at the right time is hard, and you don’t want to waste what you don’t have to bring. So if you miss your launch window, it’s like missing your train or airplane. You can’t just call up another one like a taxi, you have to wait for the next departure window to arrive, and sometimes that can be days.
Most of the answers here are mostly incorrect. The launch window is actually based on the time of year and the climate at the launch site. Altitude can also come into play. In essence, the weather conditions must be such so as to allow optimal operation of the launch window. If the temperature is too low for example, then the launch window hinges may freeze and not allow it to freely open. Fog may also form on the launch window and then the launch is pretty much scrapped. The more you know!
This will be quite simplified, but:
The Space Shuttle often went up to reach the ISS. For simplicity’s sake, let’s say that the ISS needs to be directly overhead for the space shuttle to be able to meet up with it (this is broadly true). If the shuttle launches while the ISS is somewhere else (like the other side of the earth) they’ll be orbiting the earth in wildly different places, with no way to reach each other.
I hope this helps!
Position of the Earth compared to the intended destination of the payload and the fuel required to reach destination.
There are some launch windows that are “Instantaneous”, meaning it *HAS* to launch at that time, or the payload will miss its mark. This is why they will wait 24 hours if they cannot make the exact time, for the time and destination to come back around to the correct spot again, also factoring in the travel time of the payload to reach its destination, if they miss the “Slot”, the destination may not be there when the payload arrives.
Sort of the same reason they can only launch to Mars once every couple of Years, because of the position of Mars and Earth in relation to the Sun.
Everyone’s covered the main reason in that it’s the most efficient way to get to the destination whether it be the ISS or a specific orbit.
Another reason is just the logistics. Launches require no fly zones and boats must stay out of the path to avoid the chance of having a spent rocket stage dropped on them. It’s not reasonable to keep these active for an undetermined amount of time.
Back in the 70s – earth bound scientists knew that there would be an alignment of planets that wouldn’t happen for thousands more years – way after any of our of our grandchildren’s lifetimes.
They used this opportunity to launch 2 spacecraft to observe our solar system.
These were:
https://en.wikipedia.org/wiki/Voyager_1
And
https://en.wikipedia.org/wiki/Voyager_2
Had these spacecraft not been launched when they were – we would have had to send separate spacecraft to each of the planets to have a look.
As it happened – between the 2 ships – they captured our solar system in the only chance in our lifetime of seeing anything like it.
The ‘best’ “launch window” of all time. Amazing achievement for NASA and the rest of humanity.
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