# How do you calculate cruising speed of the Perserverance spacecraft?

#### apostruk

The Perserverence Rover spacecraft travelled 472 million Km over 203 days (4872 hours) to get to Mars.

If you divide this distance by the time, you get a speed of 96,880 Km/hr ... which can't be correct.

This spacecraft departed earth at a speed of 39,600 Km/hr.

Why is there such a large discrepancy between my calculation and the actual cruising speed?

Maybe someone can point out the error in my calculation.

sam85geo

#### sam85geo

Is think that travel to Mars was done in individual stages eg: x number of hours at 39,600 km/hr; then another stage for another amount of hours at a different speed, etc, etc. I suggest trying to get detailed data on the stages i.e. distances and times. Note: speeds at each stage may be available. if so you can use the Average Mean calculation to get a "guesstament" of the average speed in km/hr. Since times are involved, I suggest using the Harmonic Mean calculation to get an average speed in km/hr. Better still, just sent an e-mail to NASA and ask how they calculate average speed for the Rover's trip; (it may be posted on their web site). Sounds like a fun project, please post any results. P.S.: any statistics text will have examples and explanation of these Mean calculations.

Catastrophe

#### matt_c_

The earth travels around the sun at 108000 kilometer an hour. So departing earth at 39600 km/hr means that potentially you could be going at 140000 km/hr relative to the sun depending which angle you leave at.

Look up "Hohmann transfer orbit earth to mars" and you might find a more detail explaination of a typical trip to mars

Catastrophe

#### Helio

Why is there such a large discrepancy between my calculation and the actual cruising speed?
Interesting question. matt_c's point is important.

The best way to see the answer is to look at the orbital speeds of both Earth and Mars. Earth is about 108,000 kph and Mars is about 86.400 kph. As an object travels from one to the other (either direction) the average travel speed will be somewhere close to the middle of these values, unless extra thrust is used.

Catastrophe

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