# Tag Info

60

Imagine you have a very heavy book and a bookcase, and your goal is to put the book on the top shelf of the bookcase. How much time would you spend doing that? Maybe five seconds, maybe fifteen. Would going much slower help you? No, it would not, because simply carrying the book is exhausting to you. You would never be able to hold the book up for an entire ...

43

Wouldn't i inevitably spiral to sun surface even if i was faster than 0km/s ? No. On reasonable timescales, an orbit will have a fixed distance of closest approach, called "periapsis." (These timescales shorten if you're close enough to what you're orbiting that an atmosphere can drag you down). You don't really need to "drop in straight line" (which ...

43

A very good question! The reason is essentially to do with tides. And a slightly over-simplified summary is: If the moon orbits more slowly than the rotation of the parent body (as our Moon does, 12 degrees per day while the Earth rotates about 360 degrees per day) then the moon will gradually orbit further and further away. If the moon orbits faster than ...

38

Primarily, locations of spaceports would change. California, not Florida would host the NASA's main launch site. Russia would be in slightly better position, able to send rockets over the Black Sea, nicer inclinations than currently available from Baikonur - although Vostochny wouldn't happen or would be closer to Chita. ESA could forget about French Guiana, ...

35

To answer your title question: By using its engines. However you seems to be quite puzzled by the fact that velocity of an object can decrease and increase over the course of an orbit. If the orbit is perfectly circular, the speed will always remain the same (until thrusters are used). However, as is the case with Chandrayaan-2, most orbits are ...

31

The Answer is on a page by Sven Grahn. No ocean going tracking ships were used. Only ground stations on the territory of the USSR. In the other answers some russian sources about the use of tracking ships were found, so the information from Sven Grahn may be partialy wrong. Short waves were used for long distance (5000 km) transmission even beyond line-of-...

28

I feel the need to correct some issues that were brought up in the other answers. Yes, gravity is an attraction-only force. But due to its relative weakness, objects in space can attain large velocities, before getting the chance to collide with any single target. In physics we would speak of excess angular momentum, which is hard to get rid of in space, ...

25

No, unless your structure is located directly on the equator and your satellite follows a perfectly circular orbit, atmospheric "orbits" aren't possible, even in a vacuum tunnel. Because the Earth is on an axis of ~23 degrees and rotates every day, it is not possible to create an orbit which has no ground track precession except for equatorial ...

24

What you're describing is (more or less) the StarTram "gen 1" design. The reference design has: 40 tonne unmanned cargo projectile, 25 tonnes of payload, ~2 m wide, ~13 m long. A 130 km maglev acceleration tunnel, evacuated. An exit point 6000 m up, on a mountain. A plasma window to allow projectile egress into atmosphere without repressurising the entire ...

23

A polar orbit can be geosynchronous and always follow the same path, but that path cannot be straight along a meridian. If the orbit passes on top of both poles, then the orbit lies on a plane containing both poles, which cuts the earth longitudinally like two opposite meridians do. However, as the satellite travels along that orbit, the Earth moves so its ...

23

The thing your're missing is that the Hohmann Transfer orbit takes time, and both Mars and Earth are moving around the sun. For the Hohmann Transfer orbit to work, the position of Mars at arrival has to be opposite the point of of Earth at Departure. The following image depicts Earth's and Mars' orbit as circular, rather than elliptical to simplify ...

19

Many novel launch schemes need some amount of help from rockets. What kills a lot of them is doing a tradeoff study of just enlarging the rocket part and getting rid of the non-rocket part. Surprisingly often, that works out to be better and cheaper. --Henry Spencer This is a system that needs a rocket part, as one of these two cases would necessary ...

18

You need below 2866 m/s of orbital velocity at 1 AU to crash into the Sun. You technically don't need to slow down exactly to 0 m/s relative to the Sun in order to crash into it. Let's calculate the approximate velocity required to graze the "surface" of the Sun. This is an excellent answer on how to calculate apoapsis and periapsis of an orbit. So first, ...

17

Ships were used to receive telemetry. Work in the ocean took place on February 12, 1961. At this time, preparations for the launch of the world's first manned spacecraft Vostok were completed. At the Control Center, a decision is made to use a tracking ships for telemetric monitoring of the onboard equipment of the spacecraft. On April 12, 1961, ...

16

And note that if you want to hit the sun the cheaper (but slow!) way to do it is to head out. 12.32km/sec will take you to infinity, at infinity a burn of 0m/sec will kill your orbital velocity and you'll come straight in. Of course this will take infinite time, but even going only as far as Jupiter's orbit means you use less energy to drop your periapsis ...

15

According to this source (in Russian; includes communication log and post-flight debriefing) the only ground stations that are listed as those that were communicating with Gagarin were located in USSR. This leads to conclusion that there were no other tracking stations located elsewhere. The list of the stations: Located at launch site (Baikonur). ...

15

I've found that language barrier problem exists. There are many info in Russian that have no proper translations in English. There were space tracking ships too. Information that USSR had not them at the time is not correct, the first ships were equipped in 1959-60. Sources: 1. http://niskgd.ru/pages/qa.htm quotes: Первые 6 судов, что начали работу до ...

15

There are two ways in which a massive orbiting body, such as a planet, can clear a smaller object from the vicinity of its orbit. One, obviously, is by colliding with it. The other, more common way is called the gravitational slingshot effect.* This is a trick that many space probes have used to gain (or lose) extra speed and thus get further away from (...

15

Such a tunnel is not plausible for a number of reasons. 1. Problems with orbits First of all, as other people have said it would only work for equatorial orbits which were either circular (very long tunnel) or had a period which is some rational multiple of the Earth's rotational period. And, again as other people have said, the real Earth is nothing like ...

10

Gravity does not cancel out at any of the Lagrange points, not even L1. As you point out, at L2 both the central body and orbiting body are pulling the same direction. But there is a third character in this tug of war, centrifugal acceleration. It's not truly an acceleration but inertia in a rotating frame. But when you're in the rotating frame it sure ...

10

Orbits beneath synchronous orbits have a higher angular velocity than their planets rotation, orbits above have a slower angular velocity. Drag (atmospheric or tidal) would try to match the angular velocity to the planets rotation. So below a synchronous orbit objects get slower, above it they would speed up (and slow down the rotation of the body they are ...

8

No, such an orbit is not possible (or: it's not possible unless the satellite is accelerated most of the time, which is not plausible in terms of fuel). In particular it's not possible for the path of the orbit to trace out a great circle over surface the Earth (in a coordinate system rotating with the Earth). Your picture shows a great circle. For a ...

8

What you are looking for is called orbit determination, and in particular batch least squares orbit determination. To learn about it I can recommend Statistical Orbit Determination by Bob Schutz, Byron Tapley and George H. Born. I understand that you want to try to do it yourself. Nevertheless, if at some point you are looking to do it with software, it is ...

8

If you define perfection as absolutely zero eccentricity then perfection is impossible. There will always be eccentricity in an orbit, even if it is very small. Orbits vary due to: Spacecraft system inaccuracy: no spacecraft is perfect, no matter how accurate Changes in the density of the orbited planet Gravitational influence of other celestial bodies: my ...

8

This would be a tunnel a couple thousand kilometers long, that extends from the surface of the Earth to approximately low earth orbit altitude at both ends, strong enough to keep vacuum inside and the atmosphere out at sea level, such that its openings are in place for a space station in a highly-elliptical geosynchronous orbit comes flying through at about ...

7

In this supplementary answer I've crudely processed all TLEs for Vanguard 1 and plotted the trends. I used the mean motion (revs/day) to get a period, divided by 0.9975 (estimating from this answer) to undo the effects of $J_2$, then used $a^3=GM (T/2 \pi)^2$ to estimate a semimajor axis, periapsis and apoapsis based on the TLE's eccentricity value. This is ...

7

The general concept of doing things slowly generally allowing better efficiency in a design is certainly correct. The difficulty with applying this to rocket launches is the concept of gravity loses that in general mean getting to orbit as quickly as possible is better. Slow/efficient space access via space elevator and related designs is the logical ...

6

In addition to Russell Borogove's good answer there is another factor here to keep in mind: When you are dealing with planets you can't just add together separate burns. If you add up the energy needed to escape Earth, the energy needed to go from Earth's orbit to Mars' orbit and the energy needed to enter Mars' orbit you will get more than 16 km/sec. In ...

6

16 km/s is about right for Earth surface to low Mars orbit, summing up a few entries in this table. I am not sure as how he did it though, and was unsure if he used the escape velocity of Earth, the Hohmann Transfer, and also if that was only that velocity computed needed to be obtained once At a minimum, this would be split into ascent to LEO (~9.4 km/...

6

After reading all your answers I'd like to summarise the situation. The black circles are the circular orbits and the red ellipse is the transfer orbit. Consider a spacecraft in the elliptical orbit. At the point P the velocity is greater than the circular orbital velocity, and that's why the distance from the centre increases. And at the point A the ...

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