# Tag Info

13

The visual acuity of a healthy human eye is about 1 arcminute (a full circle is 360°, 1 ° is divided into 60 arcminutes). A football with a diameter of 220 mm at a distance of about 775 m subtends an angle of 1 arcminute. Or a tiny object of 0.2908 mm at a distance of 1 m. The Earth diameter is 12742 km. So the distance is 43,8 million km or 0.293 AU as @...

11

According to Keplerian orbital mechanics, it will never come so close to earth "to get attracted by Earth strong enough to fall on Earth" (unless it will hit the earth directly). Everything entering Earth's Hill Sphere from "outside" is on a hyperbolic orbit, so it is going to pass earth no matter how close it passes Earth (here also: except a "direct hit")....

10

How close would the Tesla Roadster with Starman have to get to Earth in order to become attracted and fall on Earth? tl;dr: If Roadster approached the Earth with $v_{inf}$ of 3000 m/s and an impact parameter of about 24,000 km from Earth's center (about 3.8 Earth radii), Earth's gravity would deflect it just enough for a grazing collision. From Wikipedia's ...

6

Putting the spacecraft id (-143205) into the JPL HORIZONS ephemeris system produces: TRAJECTORY: This trajectory is based on JPL solution #10, a fit to 364 ground-based optical astrometric measurements spanning 2018 Feb 8.2 to March 19.1 Trajectory name Start (TDB) Stop (TDB) -------------------------------- ----------------- ----------------- tesla_s10 ...

3

The C3 was actually pretty accurate, what was not accurate was the plot that followed. The first version of http://www.whereisroadster.com used a trajectory I calculated from the C3 measurement and the time that it left orbit, which lead to something fairly close to the actual trajectory. My guess is that the image provided was wrong, probably the best ...

2

Starman will be pretty close to Mars in 2035, so if there is any good Martian telescopes then, they will be able to spot it. We could do so in October of this year, but there aren't any telescopes good enough. From Earth, January 2047 is the most likely time to spot with a 1 meter or smaller telescope. A 1 meter telescope was what last saw Starman. Because ...

2

To stay in practice I'll do the exercise that confirms what @PearsonArtPhoto's answer already says. $C_3$ the characteristic energy is twice the total energy (kinetic plus potential) $E$ of a body with respect to a larger gravitational body $$E = \frac{1}{2}v^2 - \frac{GM}{r}$$ $$C_3 = v^2 - 2\frac{GM}{r}$$ So for example, Earth is bound to the Sun so we'...

2

First of all, the 2091 date is based off an old set of orbital predictions, the next time it will be close to Earth is actually 2047. For more information, see the article I wrote for Ars Technica. For it to orbit Earth, you would have to have a particularly close flyby of the Moon, which changed the orbital energy just right to orbit the Earth in a pretty ...

1

What is the closest distance SpaceX's Tesla Roadster (Starman) will ever be to Mars? I predict 0 meters. Musk will capture the Falcon-9 2nd stage adorned with his red Tesla Roadster, bring it to Mars and display it in front of SpaceX Mars headquarters in a similar fashion to the Falcon-9 in front of SpaceX Earth headquarters in Hawthorne. I think this is ...

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