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With SpaceX's mission of getting a human colony, why would they launch the roadster into the astroid belt and not actually attempt to inject it into mars orbit?

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The time didn't line up right, and the payload didn't meet planetary protection standards. The nearest launch window opens in June of this year. MAVEN will take advantage of it. To actually go to Mars, it would have to meet planetary protection standards, and I don't think a used car would qualify.

What they did instead was to demonstrate they could go to Mars, if they launched at the right time. This, however, was not the right time to do so.

In addition, it would have required a whole lot more complex of a satellite to achieve orbit, including propulsion capability, deep space tracking, solar power, attitude control, and more complex stuff. That would bring the cost from maybe a million to tens of millions of dollars for the payload. And it would look much less like a car.

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    $\begingroup$ Also to get into orbit would require a whole bunch of other systems, including an insertion stage capable of delivering about 1000 m/s, an X-band transponder for tracking and communication, a computer, attitude sensors, correction thrusters to adjust course and for attitude control, and solar panels to operate all of that for months. And an operations team to track and maneuver the vehicle, and an agreement with NASA to provide Deep Space Network services. $\endgroup$ – Mark Adler Feb 19 '18 at 4:20
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    $\begingroup$ @ReactingToAngularVues but they demonstrated they can launch a probe which could do it. $\endgroup$ – jkavalik Feb 19 '18 at 6:23
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    $\begingroup$ @ReactingToAngularVues so... if somebody were to contract SpaceX in to delivering a payload to Mars orbit, they have proved they have the capability of doing it with more than just their word to go on. The point is that they proved it could be done, but have no need to do it just yet. Doesn't mean people aren't watching & are interested in this fact. Think of it as half test on their new platforms capabilities, half massive marketing campaign. $\endgroup$ – Trotski94 Feb 19 '18 at 10:05
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    $\begingroup$ @ReactingToAngularVues: The point is that the Falcon Heavy actually has demonstrated its ability. This was a demonstration of a launch system, not of a bound-for-Mars payload. $\endgroup$ – DevSolar Feb 19 '18 at 10:53
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    $\begingroup$ Planetary protection standards are one thing. Also if it did manage a successful orbital insertion, you'd then have a large piece of space junk in Mars orbit. With the state of space junk in Earth orbit, not doing the same thing in Mars orbit is sensible. $\endgroup$ – Graham Feb 19 '18 at 12:07
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  • The trip to Mars takes a long time
  • Entering mars orbit isn't a single burn activity, once you get near you must do at least one more burn to enter that orbit
  • The rocket engine requires liquid oxygen
  • The current design of the second stage rocket (and first stage, incidentally, but irrelevantly) does not include sealed oxygen cells. They continuously vent gaseous oxygen so the pressure inside the cell doesn't exceed its design capacity
  • The oxygen fuel would have been depleted by the time the second burn was required

So to enter mars orbit you need to have a second stage that is designed to use fuel that doesn't vent so later orbit injection burns can happen once the rocket nears the final orbit.

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This was a rocket test burn.

They wanted to see how far the system could take it - they expected to reach Mars orbit (as in, the distance Mars orbits the Sun) but actually got into a trans-Mars orbit. It was initially thought it's orbit would take it into the asteroid belt. This was revised once more data was available.

Here's Elon's tweet about it: https://twitter.com/elonmusk/status/961083704230674438/photo/1?ref_src=twsrc%5Etfw&ref_url=http%3A%2F%2Fwww.latimes.com%2Fbusiness%2Fla-fi-spacex-falcon-heavy-orbit-20180207-story.html

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  • $\begingroup$ It didn't/won't reach the asteroid belt. That was a claim which has since been corrected. Yes, perihelion will be beyond Mars but not far enough to be deemed within the asteroid belt. $\endgroup$ – Anthony X Feb 19 '18 at 23:55

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