70

In order to land on the Moon, you must, at some point, be moving towards the Moon (decreasing your distance from it, to be more precise, you may also be moving sideways) and close enough that the Moon's gravity dominates that of the Earth and the Sun. From that point on, your kinetic energy (relative to the Moon's centre of mass) can only increase as you get ...


67

Your orbit is uniquely determined by a current position (three coordinates) and velocity (three more quantities to give magnitude and direction). Going places involves changing your orbit. For instance, from a circular orbit about Earth, enter an elliptical transfer orbit to the moon, then circularize your orbit about the moon. Everything you do in space ...


54

@SteveLinton's answer is right, no matter how gently you try, by the time you get to the surface the Moon's gravity will have accelerated you to something like 2,400 m/s. There are ways to use the gravity of the Earth and Sun to make a tiny reduction in this, but it's a very small effect. The simplest way to argue this is that rocks on the Moon don't ...


53

I want to allow students to tinker around with basic central force motion and see the ways in which conic sections are altered by thrust, etc. Seeing/enacting an example of rendezvous (maybe in a CW frame?) would be neat too. I definitely think Kerbal Space Program is the right answer here. The ways in which it departs from real-world space flight (such as ...


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.


42

http://nbviewer.jupyter.org/gist/leftaroundabout/3955d27877e19be39d0f61fdafce069e Barely achieving escape velocity means you take a parabolic orbit. The thing with parabolic orbits is that they actually approach zero speed as you depart to infinite distance from the starting body. That is, zero speed with respect to the starting body's frame of reference, ...


41

More or less. While the ISS is below the satellites use for TV transmissions, it is passing by so fast that the coverage will be highly intermittent, meaning that you would be able to watch a channel for only a couple of minutes, have black outs over the oceans, and repeat. Other notable differences would be: Normal satellites receiver are "fixed": The ...


24

Personally, I teach orbital mechanics classes to preschoolers, elementary and middle school kids using a makeshift trampoline with stretchable cloth clamped to the rim. Place a heavy weight (e.g. a dumbell) in the middle to simulate a large massive body like the earth or the sun. Use marbles to illustrate a spacecraft or planets. You can easily show the ...


24

To flyby or impact Venus varies from 3.45 to 3.6 km/s from LEO for the optimal time every 19 months. Mars varies from 3.55 to 3.9 km/s for the optimal time every 26 months. So on average, getting to Venus is a little less energy than getting Mars. But not by much. It could even be a tiny bit more in some years. If you also want to get barely into orbit ...


22

The most fuel efficient way to leave the solar system at present, is to launch into a trajectory that (like that used for Gallileo) may well involve one or several gravity assists from Earth or Venus, but which eventually gets you to Jupiter. If you can get to Jupiter you can almost certainly do so in such a way as get a slingshot into a solar escape ...


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 ...


19

I spoke to Mike Lammers the Flight Director for the ISS and asked him about the mass uncertainty of the ISS; he mentioned that it is ±5000kg or about 1% of the total mass of 411,000kg. Most of the uncertainty comes from waste going back to earth. Every cargo vehicle goes back down with tons of return cargo and trash. There’s no scale on ISS so as the crew ...


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 (...


17

Uhoh touches one side of the problem: "Why" - the lower the orbit, the less of Earth is covered in a single pass, and the closer to equator the orbit, the less do the passes vary further narrowing the area. MEO equatorial satellites make sense. The lower the orbit though, the less useful they become. Still, there's a slew of tasks that wouldn't be hurt by ...


17

Theoretically, you can go anywhere in GEO for an arbitrarily small ∆v - you raise your apogee a little bit, which slows you down, wait until you've phased to your destination latitude, then re-circularize back into GEO. In practice, though, as @uhoh mentions in comments, there are stable longitudes in GEO that require more than an infinitesimal maneuver to ...


16

@Antzi's answer is right, but I'll add some context as a supplement. While Doppler (mentioned there) might or might not be an issue for an off-the-shelf commercial satellite TV box (I don't know) it could probably be fixed with a mod that NASA could easily manage. Several answers to Do astronauts get Netflix on ISS? indicate that there is access to "new ...


16

Gemini 4 was the first unsuccessful try of a rendezvous. They sought at that times it should be possible to rendezvous from a short distance by simply thrusting towards the docking object. They had to learn it the hard way that this strategy works only on very, very short distances and in a short time. The circumference of a low Earth circular orbit with a ...


16

Sunlight pressure. The acceleration is 9.08 μN / m2 (Assuming perfect reflectivity). The size is about 3.66* 12.6 = 46 m2. That gives a thrust of about 414 uN. The mass is about 1300 kg. Thus the acceleration from sunlight max is about 3.2 e-7 m/s2. Of course, there are a lot of assumptions in that, the mass is probably higher, it won't be perfect ...


16

According to Wikipedia, the delta-v requirements to stay at L1 or L2 are about 30-100 m/s per year. That seems quite high, however, more likely is around 5-16 m/s. The sun shield has an area of about 300 m^2. The thrust possible is about 0.00279664 N, assuming purely reflective. Mass of JWST is about 6200 kg. Putting all of that together, the possible ...


15

It would be lost in space. If you barely reached the moon escape velocity, it means that your object will reach an orbit somewhat similar to that of the moon. From there, the orbit will be unstable due to earth/moon (and other bodies) interactions. It might take the cargo back earth, back to the moon, or in deep space. Predicting accurately theses orbits ...


14

The long comment chain below this answer highlights the mis-conception that NASA astronauts as a whole did not understand the orbital mechanics of docking. As this comment points out, the mechanics was well understood at the time, and at least one astronaut had written a thesis on the topic a few years earlier: ... Aldrins thesis about orbital ...


14

The mass of the Voyager is $\approx$ 825 kg. The mass of the Jupiter is $\approx 1.9 \cdot 10^{27}$ kg. According this question, the Voyager accelerated from $\approx 10.2 \frac{km}{s}$ to $\approx 27.8 \frac{km}{s}$ by its Jupiter flyby at 1979.7.29: Thus, the Voyager got $\approx 17.6 \frac{km}{s}$ velocity from the Jupiter by its gravitational slingshot ...


14

The second table here essentially answers your question. Venus transfer from Low Earth Orbit is 3.5 km/s, Mars transfer is 3.6. This will allow you to impact either body (on Venus you will need to make sure your vehicle is tough enough to actually impact, rather than dissolving in the atmosphere, but that's not really the point). In either case, you can ...


13

There are typically five planned trajectory correction maneuvers on the way to Mars, referred to as TCM-1 to TCM-5. (Also there is a slot for an emergency TCM-6 a few hours before entry, but it is not expected to be used.) Also I sometimes refer to launch as TCM-0. That's the really, really big TCM. TCM-0 provides the energy to place the aphelion of the ...


13

The “westward penalty” from Kennedy/Canaveral would be about 800 m/s of delta-v, about 8-9% of the total delta-v requirement to orbit. Most crewed launchers intended for LEO to date have not had that much performance in reserve; a shortfall of only 100 m/s from LEO usually means prompt reentry. Atlas/Mercury and Titan/Gemini could not have managed it. The ...


12

If you're already in a solar orbit, then yes. You can use a sail at an angle and send the reflections prograde. The result is to reduce your orbital energy and you spiral in. I recall it was a standard physics problem to find the angle that maximized the energy transfer (it's not 45 degrees). Time of journey depends on the mass of your item and the ...


12

UC Boulder has a project, PhET, that has many free, interactive, in-browser math and science modules. They have one called Gravity and Orbits that's written in HTML5, making it compatible with most modern browsers (including Safari on iPads). If you click the 'For Teachers' drop-down, you'll find it even has quite a few resources for lesson planning with ...


12

Spaceflight Simulator An Android software, but it's possible to run it on a PC as well. It's 2d, so it's much simpler to use than 3d software. There are some premium features ($4 unlocks all of them forever), but the free version is enough to launch missions to all the planets in the inner Solar System, and to put space stations in orbit and dock to them. ...


12

Escape velocity is the velocity at a given altitude (usually the surface) that is enough to leave the body's sphere of influence with a positive net velocity. But if you leave a body at exactly escape velocity, your velocity bleeds off as you climb in exchange for gaining gravitational potential energy, and your velocity tends to the limit of zero at ...


12

If you want to avoid gravity assists, the most fuel-efficient way out of the Solar System is to launch due East from from a launch site in the Ecuadorean Andes, sometime before local midnight on a January 3 when there's a new moon. This gives you the maximum possible benefit from the Earth's movement, leaving only about 12,000 m/s of delta-V needed in ...


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