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 ...
48
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.
47
Delta-V to LEO is about 10 km/s. From there to C3 (Earth escape) is another 3.2 km/s. It's just another 30% delta-V.
The problem is the Tyranny of the Rocket Equation. More delta-V means more fuel. More fuel means more mass. More mass means more fuel.
How much more? Fuel costs scale according to $e^{\frac{\Delta V}{v_e}}$, that is e to the power of the ratio ...
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
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 ...
42
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 ...
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 ...
40
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,...
39
Why is it the most energy efficient to change orbit inclination while crossing the equator?
Specifically, it's most efficient to do a plane change at one of the two "nodes" where the origin orbital plane intersects the destination plane. ANASIS-II is destined for geostationary orbit, so its destination plane is the plane of the equator.
Any orbit ...
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 ...
34
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 ...
34
It's not hard, it's just expensive. We know exactly how to do it. Compare this to building computer processors with 1nm transistors, or making reliable self-driving cars. Those are both things that we currently don't know how to do, and we don't even know exactly how to get better at doing them.
Even going past low Earth orbit to another planet, like Mars, ...
34
After writing my comments, I started writing a new answer. That got long, so here's a shorter one.
The "energy of an orbit" may be poorly defined and depending on the definition, is not subject to energy conservation laws. Let's ignore it and focus on the kinetic energy.
Kinetic energy is not necessarily conserved. Momentum is. Momentum (derived ...
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 ...
31
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 ...
29
A great aid to intuition is to remember one principle about orbit changes: if the engine is off, the orbiter always returns to same point one orbit later.
So for any orbit change, if you want to do only a short burn, it has to be at a point that is common for both the current orbit and the destination orbit. This applies to inclination changes, altitude ...
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. ...
24
This conclusion MUST have been reached by NASA (or even NACA) in the leadup to the Apollo landings.
Despite the name, getting people to the Moon is not rocket science. It's rocket engineering. Engineers know that effects that are orders of magnitude smaller than the sensitivity of their systems are essentially non-effects. General relativity is a non-effect....
23
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 ...
23
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 ...
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,...
23
What's the root cause of the disparity between what the article says and what's shown in the video?
There is no disparity. The article says you need a minimum velocity of two inches per second [bold emphasis mine]:
The engineer added, “Simple trigonometry led to the conclusion that pushing an object away at two inches per second within a 30-degree cone ...
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 ...
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
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 ...
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
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
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