The Stack Overflow podcast is back! Listen to an interview with our new CEO.
49

Yes, Trajectory Correction Maneuvers (TCMs) are always performed during cruise phases, whether before or after gravity assist flybys. This NASA tutorial serves as a good general reference. One source of error resulting in an imperfect trajectory (one that would miss its aimpoint at the next destination, whether the ultimate destination or an intermediate ...


46

That's a mistranscription of OMS Burn, or Orbital Maneuvering System burn. The OMS system is how the shuttle changed its orbital characteristics. You can read about it here. One, two or more might have been used to fine tune the orbit, avoid space debris, rendezvous with the space station, etc.


43

All interplanetary probes that I am aware of were launched into a parking orbit, and then waited some time in that orbit before restarting a stage or igniting another stage to inject on the desired outgoing asymptote. This is done for convenience to allow long launch windows on days in the launch period. It is possible and slightly more efficient to launch ...


42

The Juno spacecraft has no means to directly measure and compute that it is in orbit. It did not send any such confirmation message. All it sent was an FSK tone indicating that it had completed the activities it was commanded to do. After the spacecraft turned back to Earth, it transmitted all of the recorded engineering data from the event, providing much ...


38

Understanding the Principle Let's start by understanding the mechanism of a gravity assist. As a spacecraft approaches a planetary body, it gets affected by the planets gravitational pull. Getting nearer, the pull increases, and eventually when the spacecraft passes the planet, the pull decreases. If you think about a stationary planet as an absolute ...


36

No, because there's nothing like water for a keel to work against. In water sailing there are two force vectors, the vector from the reaction of the wind against the sail, and the vector from the keel and rudder against the water. These vectors add together to propel the sailboat. This works for almost any direction on the compass except where the wind ...


35

If you watch these videos: ATV boost Zvezda boost ...you can see that the acceleration is quite gentle, but definite. The astronauts do need to hang on to something if they don't want to drift to the back of whatever room they're in. The first video was a reboost performed with the ATV service ship, as described in this article. Depending on what ...


34

The easiest to see ISS orbital reboosts is by checking Height of the ISS (where with height they mean orbital altitude above mean sea-level) over at Heavens Above. For example, for the last year, this is the graph: This plot shows the orbital height of the ISS over the last year. Clearly visible are the re-boosts which suddenly increase the height,...


33

You cannot directly propel the solar sail towards the sun. A solar "sail" is basically a mirror. The analogy of wind and sails on ships is not useful for understanding how solar sails work. Each photon from the sun which strikes the sail is reflected. Each photon imparts a small amount of momentum. If the sail is pointed directly at the sun then you get ...


32

Page 331 in the Shuttle Crew Operations Manual, an official NASA astronaut training document, confirms that The deorbit burn usually decreases the vehicle's orbital velocity anywhere from 200 to 550 fps, depending on orbital altitude. The deorbit burn was not intended to reduce the Orbiter's velocity to a small value, but rather to change its orbital ...


31

This was one of the questions just now during the Rosetta press briefing. This video was shown during the presentation: The triangular trajectory are hyperbolic orbits with respect to the comet and they'll (also, among other tasks also mentioned in the image you're attaching) serve to establish its mass. In essence ...


29

If you're just looking for an intuitive handle on it, try this: In circular LEO, your orbital period is about 90 minutes. If you apply a velocity change of 90 m/s, then wait half an orbit -- 45 minutes -- you should expect to be out of position by 90 m/s * 45 min * 60 s/min = 243,000m, or 243km. The distorting effect of Earth's gravity means that the ...


25

This is actually somewhat easier than you would think. In the world of Orbital Dynamics, you only have to accelerate or decelerate your orbit to move closer/further away from the object you are orbiting. So, all you have to do is create a net momentum that pushes to slow down your orbital velocity. However, a big part of what makes tacking work is the fact ...


24

As @Ame mentioned, the rocket didn't have enough fuel to put it there in one shot, like most US/Russian rockets do. However, the actual physics behind the orbital maneuver is slightly different than described. Specifically, the physics is called the Oberth effect. The short explanation of this is that a rocket thrust is more effective if done at perigee. ...


23

FORMOSAT-5 was deployed directly to a 720 km circular orbit, with only a single burn. In order to do a circular orbit so high, one has to have a more vertical ascent then would be typical. Basically, one has to be burning a significant amount of time near the apogee, which has to be 720 km in this instance. For a lower perigee insertion orbit, say 200-300 km,...


22

Does it have any additional thrusters? Not to thrust towards its targets. For that, it's 100% ion thruster propelled. It does also have a set of 12 MR-103G variable thrust (0.9 N maximum) RCS (Reaction Control System) hydrazine monopropellant thrusters that launched with only 46 kg of propellants (read: total thrust of its RCS doesn't provide the spacecraft ...


22

The answer to the question, "Do the astronauts feel the station moving?" is yes, definitely, but sometimes in an "indirect" fashion. During Space Shuttle mission STS-109, when floating in my sleeping bag and waiting for slumber to come, I would notice that occasionally my body would softly brush up against one side or the other of said sleeping bag. A ...


21

This is a large question, but we can certainly boil it down. You need several levels of requisite knowledge. I'll break it down as so: Relevance of Delta v for propellent budget Conversion between gravitational potential and its corresponding velocity The basic physics of Hohmann transfers Non-ideal factors going from surface to orbit Not all of these ...


21

There are several reasons why Satellites need to orbit Earth before they go interplanetary... The first reason: The launch site is very rarely in the right position to start an interplanetary flight. Earth rotates on a tilt, so a launch has to be timed when Kennedy Space Center crosses the ecliptic plane (the general plane that most planets orbit on). Also, ...


21

Using attitude determination devices, (including doppler shift of radio signal from Earth), it can determine* its location and velocity relative to Jupiter, and from that data, and knowing Jupiter mass, trajectory can be calculated. If the trajectory forms a loop around Jupiter - it's an orbit! * the actual determination is performed on Earth, Juno just ...


21

How small do you want to get? $F=G{Mm \over r^2}$ applies regardless of size. If you remove enough disturbances from other bodies you can get two neutrons to orbit a common barycenter on gravity alone - or send them against each other on a near-miss trajectory and they'll pass influencing each other gravitationally in essence performing a slingshot against ...


21

Actually the answer is a bit more complex than "Earth orbits at 30 m/s, so you have to stop that velocity and drop in. Thus the delta-V is 30 km/s." The question states that you start from Earth orbit, and that makes a big difference. Let's assume an almost ideal situation: the object to be sent to the sun is in a 200-km (Low!!) LEO, whose orbit plane is ...


20

The first trans-Earth injection from the moon was a high-stakes maneuver; if the Apollo's SPS didn't fire, the crew would have been stuck very far from home. I always took "please be informed there is a Santa Claus" to mean something like "we got what we wanted for Christmas" -- that is, a good burn and a good chance to get home. Basically, a seasonally ...


19

Launches from Baikonur Cosmodrome are tilted to a higher inclination than the site's azimuth to the equator (roughly 46° North depending on the individual launchpad used) to avoid the early launch ground track going over the territory of China in case of an aborted or failed launch, so any booster rockets don't fall on the Chinese territory and can be ...


19

Reversing direction is a special case of inclination- / plane-change. Here's one way to find a better upper bound on the necessary delta-V for a 180 degree plane change: Assume a 2-body system (i.e. ignoring the sun and moon). Burn once to increase your orbital energy to C3 = 0 (i.e. escape velocity), coast out to an infinite distance where your velocity ...


19

Why zero excess velocity? Well, with almost zero excess velocity you can stay near Earth, but not too near. For example, the Spitzer space telescope did this to communicate with Earth while avoiding radiant heat from Earth. It's been drifting away, but slowly enough that other factors first reduced its effectiveness.


18

In short, no. The reason is, the hardest part by far of getting to space is getting to Low Earth Orbit. As the saying goes, once you've done that, you're half way to anywhere. It would be difficult to make the elevator stay put to non-anchored locations. Furthermore, it would mess with the speed required to get to each of these locations, and in the end, ...


18

Here is an approximate but quite accurate solution. This assumes that the orbit about the departure body is aligned with the outgoing asymptote of the Hohmann orbit, which is the standard practice when putting a spacecraft in a parking orbit by a launch vehicle before its escape maneuver. This also assumes that the bodies' orbits about the Sun are circular ...


18

Yes. It is considered (sorry I don't know exactly how much, but probably a LOT - they track the torque on individual bolts during construction for example). They had an accident a while ago where a thruster started firing and oscillating wildly, causing the whole station to wobble and shake, a bit like they do in KSP. Although the forces applied exceeded ...


18

Since the questioner also asks "why are two needed" and the other answer didn't address that: Early shuttle missions flew a "standard insertion" ascent. This required two burns of the Orbital Maneuvering System after the main engines shut down and the external tank was jettisoned. The first burn (OMS-1) raised the apogee of the orbit, and the second one (...


Only top voted, non community-wiki answers of a minimum length are eligible