**(UPDATED 1.04)** Scroll down to the bottom of the post for the final review of responses.

**(UPDATED 24.03)** We got a query earlier this week via Facebook from a past participant (thanks, Massimiliano!) in one of our SocialSpace events (the Astro Luca Tweetup in 2014).

His question related to ExoMars, and – we have to admit – it was a bit of a stumper! But even if we on the ESA SocMed team didn’t know the answer, we knew who would: the flight dynamics wizards at ESOC!

No ESA satellite reaches its destination without the ‘spacecraft navigators’ – the flight dynamics experts who predict and determine trajectories, prepare orbit manoeuvres and determine satellite attitudes and pointing (read more).

So we passed the query over to Frank Budnik, who is part of the ‘FDyn’ team supporting ExoMars, and asked him to reply, which he has done.

Now, BEFORE we post the answer, first read the question and see if you can answer it without reading Frank’s reply. 🙂

**Question on ExoMars**

*Hey Daniel, may I bother you with another question? On the ESA website I have read that the entire cruise of ExoMars is 500 million km in 218 days… that means it goes at a speed of 95,500 km/h! How is it possible? The actual record of speed is New Horizon’s, almost 56,000 km/h…*

**What do you think?**

Go ahead and submit your answer as a comment to this blog post.

Next week, we’ll post Frank’s reply, and whoever has posted an answer that most closely matches his gets an ESA tee-shirt.

Cheers and have a great weekend!

UPDATE 24.03 – FRANK’S REPLY

Wow! Thank you for the large number of very well thought-out, well-reasoned and imaginative answers posted below. This query unexpectedly caught a lot of people’s attention and we were really delighted to see the range and extent of replies submitted. Our answer to the query above is in several parts.

First, before we get to Frank’s reply, take a moment to read the excellent description of orbital mechanics contributed by ESA mission analyst Michael Khan as a reply to a query from Yasmin Tayag in New York (*though, like this post’s editor, she’s originally from Toronto! – Ed.*), who blogs over at Invserse.com. Here are some pertinent quotes, although her entire post is worth reading:

## I Went Searching for the ExoMars Probe and Found the Truth About Space Highways

*An interplanetary transfer from the Earth to another planet (in this case, Mars) is not a matter of flying on a straight line with a given cruising speed like an aircraft would on the Earth, or like a ship that cruises through the ocean, with some changes in direction at given waypoints. That’s not the way it works in the solar system.*

…

*Now, on the elliptical transfer, the spacecraft it climbing away from the Sun towards the Mars orbit, and the Sun is holding on to to the spacecraft with its gravity. So as ExoMars is climbing, its height energy increases. Therefore, the motion energy must decrease. The total energy stays the same. So on its flight to Mars, ExoMars continuously gets slower and slower.*

…

*The most important thing you see is that the ExoMars trajectory, like all trajectories in space, is distinctly curved. There are no straight lines in space. Once you have bodies that have mass, such as stars and planets, you have gravity, and in the presence of gravity, everything will fly on curves. Curves are natural, straight lines are not. The distance covered following the curved red line from Earth to Mars is about 500 million kilometres, to put that into perspective. Half a billion kilometres.*

These are just a couple highlight extracts – do read the entire post!

Now to continue with our explanation, take a look at the chart below, which Frank sent over just prior to lift off.

This shows the same thing that the YouTube animation at the top of this post shows, and that Michael’s reply to the US blogger mentioned: ExoMars/TGO follows a curved elliptical path between Earth and Mars, and this distance amounts to, roughly, 500 000 000 km.

The chart shows this as a linear function of accumulated heliocentric distance (that is, distance travelled with respect to the Sun) covered with respect to time (while the YouTube animation shows the same path with respect to space). On 14 March, launch day, the total distance covered is 0. By early June, it will be 200 000 000 km; by early September 400 000 00 km and by arrival day, 19 October, just a tad under 500 000 000 km.

ExoMars/TGO heliocentric travelled distance Credit: ESA/F. Budnik

In fact, you can use this chart as a handy (although admittedly rough) reference guide throughout the interplanetary transfer. My eyeball tells me that today, 24 March, the craft has travelled about 20 000 000 km with respect to the Sun (while the YouTube animation above tells me that it is still about 126 000 000 km from Mars).

The craft will from now on steadily slow down (note that the line in the chart above is not perfectly straight) and it heads along an ellipse 500 000 000 km long to meet up with Mars on 19 October, all with respect to the Sun.

Before we finally get to Frank’s answer, take a look again at the YouTube animation at the top of the post. Note that, roughly speaking, ExoMars/TGO ‘hops off’ of Earth on launch day, arcing further out from the Sun than Earth’s orbit, with Earth thereafter pulling steadily ‘ahead’ as it remains on its tighter, faster solar orbit.

As the spacecraft arcs further from the Sun, it slows down (although you can’t really see this very well in the animation), which confirms what Michael described, i.e., that whatever its initial heliocentric speed, it continuously slows down as it travels.

Importantly, however, it is travelling, with respect to the Sun, *faster* than Mars. As you can see toward the end of the animation, Mars in effect ‘catches’ the craft, which will have to use its main engine on 19 October in a lengthy 134-minute burn to slow itself by a whopping 1550 m/second in order to slow down enough to be captured by Mars gravity.

OK, enough background… here is Frank’s answer!

========================================================

## Reply from Frank Budnik, ESA Flight Dynamics Team

*You have to compare the right numbers, which, in the case of spacecraft velocity and velocity records is not that straightforward.*

*The usually quoted record speed of New Horizon is 16.26 km/s (58 500 km/h), which is the escape velocity relative to Earth. It is true that up until now no other spacecraft has been launched at that speed relative to Earth.*

*To get New Horizons’ (approximate) heliocentric speed (i.e. relative to the Sun) shortly after launch, you also have to add the 30 km/s heliocentric velocity of the Earth – giving ~46 km/s relative to the Sun. This is an impressive speed; however, it is no longer a record speed. The record for the largest heliocentric speed of a spacecraft is held by the Helios II spacecraft, which had a maximum heliocentric velocity of more than 70 km/s!*

*ExoMars’ heliocentric velocity is not anywhere close to that (but it is still fast 😉 )*

*Taking the quoted numbers of 500 million km in 218 days (precisely, 218 days 16 hours 56 mins from separation from the Breeze upper stage at 20:13UTC on 14 March until the Mars orbit insertion burn at 13:09 UTC on 19 October) gives an average heliocentric speed during cruise of 26.5 km/second, which is somewhere between the average heliocentric speed of Earth (30 km/s) and of Mars (24 km/s), as it should be.*

*I hope this makes it clear!*

*Regards,*

*Frank*

========================================================

If this helps, here’s a quick run down of the math:

- distance = 500 000 000 km
- time = 218.67 days = 5248 hours = 314 885 minutes = 18 893 088 seconds

speed = distance / time

speed = 500 000 000 km / 18 893 088 seconds = 26.5 km/second

=======================================================

Note that this will be an average speed and, as Michael points out and as mentioned above, the craft’s speed will steadily slow as it proceeds along its path to Mars; but the line in Frank’s chart above is almost straight so this slowing is very modest.

**Summary**

It’s clear from Frank’s explanation and chart, and from Michael’s comments, that the important factor in the calculation of ExoMars/TGO speed is fixing a frame of reference, and this means using the Sun. We do this because gravity has by far the biggest effect on the spacecraft’s speed from now on (its own engine will have an effect, too) and the No. 1 source of gravity in our Solar System is, no surprise, the Sun. Massimiliano’s original question that referred to New Horizon’s speed was a bit of a red herring because the speed cited was with respect to Earth; ExoMars/TGO’s average speed of 26.5 km/second is more than enough to cover the 500 m km in 218 days – and we all look forward to its engine working rather well at the right time!

We’ll take a couple days to review the answers below and select those that came closest to including all or most of the points mentioned above.

That’s the end of our quiz challenge! Any replies posted after the date/time of this update (18:45 CET 24 March) are not eligible to win a tee-shirt. But you’re welcome to post comments!

Have a great weekend!

**===================== FINAL UPDATE 1 April**

Having reviewed all the answers, many (most!) of which were very well done, we were able to select the ones that came closest to the answer provided by ESA flight dynamics expert Frank Budnik. In fact – there were a lot!

In the end, since the key point in formulating any answer was to realise that, as some of you mentioned, all speed is relative, and the most important first step is to select a consistent frame of reference, we decided to ‘select’ any answer that gave sufficient indication of this realisation (even if the subsequent calculation was a little off). So, without further ado, congratulations to:

- Thomas
- Andrea
- Miguel Rosa
- Davide Tascone
- Ardelean Calin Petru
- Nicu
- Daniel Bandy
- Marco
- Ed
- William Easdown
- Michele
- Phil
- Dan Levesque
- Anchal

You are invited to send an email to contactsocialspace@gmail.com with your name, postal mailing address and tee-shirt size – we’ll get a shirt mailed out to you right away.

And thank you very much for responding!

– *Daniel*

## Discussion: 34 comments

subdirectory_arrow_rightAccording to https://en.wikipedia.org/wiki/New_Horizons, New Horizons was launched at a speed of some 58,000 km/h. During its escape from Earth’s gravitational influence, that speed must have gone down again. However, on its course to Pluto it also performed several gravity assists, during which the speed must have been a lot higher than at the top of the gravity well. So it may have been going faster than that at some point during its course.

However, it looks like ExoMars is taking a direct route without any gravity assists. From launch onwards, it only moves higher in its orbit around the sun, so it goes slower and slower. Then how can its average speed of 95,500 km/h be larger than its launch speed, which we know to be less than New Horizons’ record of 58,000 km/h?

The answer must be that these speeds are measured differently: a speed is meaningless without a frame of reference. Presumably the 58,000 km/h launch was measured relative to the Earth’s surface. But I would think that the 500 million kilometres were measured in a frame of reference that does not move or rotate with the Earth, but rather stays centred on the sun. In that frame of reference, the Earth is not stationary. That means the ExoMars launch vehicle did not start at a speed of zero, but was going about 107,000 km/h before it even left the launch pad!

subdirectory_arrow_rightIn the video, it shows a travel distance of only 143 million km. So based on that distance, you get average speed of around 27,000 km/h. Also, ExoMars needs to “stop” at Mars. New Horizons kept on sailing right past Pluto, as it was travelling too fast to stop with the resources on board.

Other than that, I’m not a rocket scientist! Wish I was though.

subdirectory_arrow_rightAs earth travles at an immense speed around the sun which is like 7 times speed of bullet the exomars even before it liftedoff from the surface of earth it was travelling at the same speed with respect to the sun.As it lifted off it was at same but its all relative and the speed decreased to 95,000kmph.New Horizons did several gravity assists which decreased its speed but corrected its course.As Exomars is taking a direct path through a frictionless vaccum(space)it has no force opposing it.The vehicle might have orbited earth im not sure but if it had its speed must have been much slower so it takes a direct path.The distance Is represented as the earth is still from the point of release but mars is moving so it depends on that factor.

subdirectory_arrow_rightI suppose it’s because new horizon’s speed at launch was relative to earth, since the record talks about speed at launch, while whe calculating the cruise speed for exomars it is absolute, or rather relative to the sun, so you have to take into account the launch speed + the speed of earth moving around the sun + the speed of the earth rotation on the surface, which is a lot 🙂 also that’s why rockets are always launched towards East, to leverage on that rotation speed

subdirectory_arrow_rightIf it’s true the simplest answer is often the right one, then this is my guess: that “500M km” on the blog post is an error 😀

Earth and Mars opposition is about 50M km right now, so even if I’m aware that you can’t go on a straight line 500M sounds too much…

Not mentioning that the video above shows a path length of circa 140M km.

My t-shirt size is M, thank you 😀

subdirectory_arrow_rightAliens, obviously.

subdirectory_arrow_rightAround 21000 km/h I think

subdirectory_arrow_rightBecause Mars is also moving at 86.000km/h, Exomars will in fact need to do an absolute distance of 141M (Earth to Mars distance) + 86k x 218 x 24 (Mars travel) = 500M km

Exomars starts at 107k km/h (Earth speed) but a month later will be around 50k, and another month 30k, and by mid August 15k to arrive near Mars at 9k. Average relative speed 27k. Absolute 95.5. Good thing Mars moves slower than Earth and also starts ‘behind’ Exomars.

subdirectory_arrow_rightCorrection: actually Mars does 449M km in 218 days, so the total would be 590M. This 90M difference should be mostly from Mars starting ‘behind’ and a bit from non parallel trajectories to rendezvous point.

subdirectory_arrow_rightThe thing is Earth, in the time ExoMars needs to get to Mars, will travel half of its orbit around the Sun, and Mars will travel a quarter of its orbit. So, even in now the distance is of 500km, it will substantially reduce during ExoMars’ journey to Mars

subdirectory_arrow_rightTo leave Earth Gravity field the TGO must have reached about 40.000km/h.

16 october it will arrive near Mars at about 20.000 km/h

subdirectory_arrow_rightIt’s about the system of reference, depends What you count when say the speed. This ExoMars speed is for Earth, the NH is for Sun.

subdirectory_arrow_rightRoughly 4.3 KM/s so that’s 15480 KM/h. That’s my guess.

subdirectory_arrow_rightThat is considering the earth as the reference point. The earth’s orbital speed is 107200 km/h. If we add a change of dV of 15480 km/h, which is the amount needed to get to a Mars Transfer Orbit, we get 122680 km/h. ExoMars is on an escape trajectory from the Earths gravity, but it is being slowed down. First by the gravity of Earth, then by the gravity of the Sun, since ExoMars is traveling to a higher orbit.

The avg. orbital speed of Mars is 86700 km/h. Assuming a perfect Hohmann Transfer, the final speed of ExoMars will be 86700 KM/h as well. So ExoMars started from 122680 km/h, will get slowed down by Earths gravity to a few hundred km/h over 107200 km/h (the Earths orbital speed), and then got further slowed down by the Sun’s gravity until it got to the orbital speed of Mars: 86700 km/h. The average between 107200 and 86700 is 96950, so it’s not unreasonable to think that the average speed of ExoMars is 95550 km/h. This is my full answer.

subdirectory_arrow_rightI posted this again just because the other answer I split in two and I didn’t like that. Hopefully I still qualify for the contest!

All following speeds are relative to the Sun.

The earth’s orbital speed is 107200 km/h. If we add a change of dV of 15480 km/h, which is the amount needed to get to a Mars Transfer Orbit, we get 122680 km/h. ExoMars is on an escape trajectory from the Earths gravity, but it is being slowed down. First by the gravity of Earth, then by the gravity of the Sun, since ExoMars is traveling to a higher orbit.

The avg. orbital speed of Mars is 86700 km/h. Assuming a perfect Hohmann Transfer, the final speed of ExoMars will be 86700 KM/h as well. So ExoMars started from 122680 km/h, will get slowed down by Earths gravity to a few hundred km/h over 107200 km/h (the Earths orbital speed), and then got further slowed down by the Sun’s gravity until it got to the orbital speed of Mars: 86700 km/h. The average between 107200 and 86700 is 96950, so it’s not unreasonable to think that the average speed of ExoMars is 95550 km/h. This is my full answer.

subdirectory_arrow_rightNew Horizon’s speed was not an orbital speed, it was its speed relative to the Earth. Its “escape speed” if you want to say so. ExoMars’s speed is its orbital speed. Its maximum speed relative to Earth was 12.1 km/s after the last stage of the Proton rocket finished firing.

subdirectory_arrow_rightMaybe because the distance between Earth and Mars changes…the distance between the Mars orbit and the Earth orbit goes from 58 to 100 milion km so maybe the 500 million km that Exomars has to fly are calculated relatively to the Earth movement and are not effectively 500 million km but more less…

subdirectory_arrow_rightAfter some reflection:

Mars is moving at 86.000km/h so it will make 450M km in 218 days. Exomars will do 500M km because of different trajectory and will do an absolute average speed of 95.500km/h. So Mars starts ahead of ExoMars on the ‘race’ to the rendezvous point but runs slower.

As for relative speed, ExoMars starts at 107k km/h (earth speed) but a month later will be at 50k, another month later at 30k, by mid August at 15k and will arrive near Mars at about 9k (but close to absolute 86K – Mars speed).

Average relative speed 27k. Absolute 95.5k.

subdirectory_arrow_rightAnd after some sleep and to conclude: 141M km is the distance in direct line to the adversary (Mars) and 500M km the distance to finish line (rendezvous point) in this ‘cosmovelodrome’ 😀

subdirectory_arrow_rightThe probe already has am Earth`s orbital speed all the further trust is to escape Earth`s gravity and to adjust its orbit to intersect with Mars. For New Horizons probe the speed is given considering the frame of reference on Earth.

subdirectory_arrow_rightmaybe, the 500 000 000 km are an estimate for the total way until there is no chance anymore to keep ExoMars in a stable orbit.

So, in my opinion, the first 141 000 000 km (seen in the video) are the direct route to mars.

When ExoMars finally arrives, it will “enter an elliptical four-day orbit around Mars, taking it from about 300 km at its nearest to around 96 000 km at its furthest point”. when you turn this ellipse into a diamond and add the radius of mars (3396km), you get about 4* sqrt((99396km)^2 + (3696km)^2) = nearly 400 000km per orbit.

“After a year of complex ‘aerobraking’, manoeuvres during which the spacecraft will use the planet’s atmosphere to lower its orbit slowly to a circular 400 km”. With this, its possible to calculate the change of orbit length:

400 000km -x * 365day = 400 km -> x = 1095km/day

So the total distance ExoMars is flying in the year mentioned above: 400 000*365 -(1095/2) *365^2 = nearly 73 000 000km

Now there are still 286 000 000km. and this distance, ExoMars could get by flying a long time around mars 🙂

if my idea is wrong, im not sad. It was fun to think about it.

subdirectory_arrow_rightThe video says 140 millions km but exomars is not going straight, but doing almost half of an ellipse which size is between earth and mars radius … So if we say a circle of 225 000 000 km radius in 214 days this will give around 38km/s. A (or 137 000km/h, which is absolute speed not getting away from the sun). I over estimated a bit so lets go for 36km/s or 130 000 km per hour !

subdirectory_arrow_rightWhile I’m unable to find the ExoMars escape velocity, I’ll take a guess

The referenced speed for new horizons was an earth-centric velocity at the end of its escape burn. ExoMars doesn’t require such a large escape burn as it does not need to escape the sun like new horizons did.

The discrepancies in speed come from changes in frame of reference. Relative to the sun the earth travels at ~107000km/h and Mars at ~86000

As such the spacecraft’s velocity relative to earth will only be a little over escape velocity however in the Suns frame of reference it’s speed will be the earths speed plus the extra over escape velocity.

The craft starts out well over this averaged 95500 km/h but slows down as it fights the Suns gravity and flies outward. As such the overall average speed relative to the sun-which is the frame of reference for the distance-is 95 500 while the earth-centric speed is much much lower

subdirectory_arrow_right42674 km/h

subdirectory_arrow_rightWell, exomars will reach tangentially mars’orbit, it means that TGO should have a little more of mars’ speed. In 7 months, the time needed by the probe to reach mars, the planet will be at aphelion (between september and october) with its minimun speed (referring to the sun). So the TGO should have more or less the same speed wich is 22.000 km/s

subdirectory_arrow_rightOh yeah, I’ve seen a movie that deals about this question: a big truck full of sweetness runs away and the whole world try to achieve it.

It’s name is Mad Mars: fury road

subdirectory_arrow_rightAll speeds are relative – there is no such thing as absolute speed (unfortunately). New Horizons holds the record for the fastest launch speed from Earth, since it was launched directly into earth and sun escape trajectory at 59k km/h (relative to the Earth). Voyager 1 went faster after its Jupiter gravity assist at 61.3k km/h (relative to the Sun). The Helios satellite travels fastest (relative to the Sun) due to its highly elliptical orbit (so its velocity keeps changing; it’s fastest when closest to the Sun).

Since ExoMars was launched on a Proton/Briz-M, there is no way it could be the fastest launch. In fact, previous blogs have explained the multiple manoeuvres required due to the (relatively) puny thrusters available. It is more likely there is something wrong with the question.

It could be the distance, or the time that is wrong.

The graphic at the top of this blog shows a 141M km distance from Earth to Mars, over 218/9 days, suggesting the distance part is wrong. That would give an average speed of 141M/219/24 = 26.8k km/h.

The blog that gives the 500M km figure is not clear what this number refers to. If we take the 500M km figure as the distance from launch until aerobraking in Nov 17, (which is how I read it) then the time is wrong, and the duration is actually approx 610 days (counting whole months), which gives an average speed of 500M/610/24 = 34.2k km/h.

These are only average speeds over different distances and could therefore both be right. Given the final post launch velocity is quoted as ~33k km/h, then I’d give more weight to the second figure.

subdirectory_arrow_right55.000 km/h

subdirectory_arrow_rightI haven’t read any of the other comments at all so as to not bias my answer. I reckon it’s because the speed of New Horizons is measured with respect to a different reference point than the distance travelled by ExoMars is. I think New Horizons’ speed is measured with reference to the Sun, but because 500 million km is the distance between Earth and Mars, ExoMars’ speed is calculated with reference to those. If you calculated the speed of ExoMars with reference to the Sun I think it would be a lot lower and well below New Horizons’ record because ExoMars doesn’t need (or want) that amount of speed, which would put it on a trajectory to escape the solar system, to get to Mars.

subdirectory_arrow_rightThe speed depends on the system we use as reference. So it’s plausible, if we take the sun as reference. It’s more complex than it seems to calculate average speed so.

Anyway, I verified that the distance that ExoMars has to travel to reach Mars is ~500M. As I’m still in high school I did it with my small knowledge but with a lot of interest. I saw that Mars from 14 march to 21 october (when the rocket reaches Mars’ orbit as ESA set) travels 3/8 of its orbit, that is about 536×10^6 km (used https://www.solarsystemscope.com/ ).

Then, using Pythagorean theorem (also if the results are hugely approximated, I found the distance from launch point to landing point , using the distance between Mars and launch point (given by your video: 141×10^6 km), and the distance traveled by Mars that I found.

√(((141×10^6)^2)+((536×10^6))^2)=~5.5×10^8km!

So, finding average speed from Earth is much difficult and useless as both Earth and the rocket are moving constantly at different speeds.

This is my thought and I hope to get your fabulous t-shirt! 🙂

Thanks for your work ESA!

subdirectory_arrow_rightThis is a great question and one I have never previously given much thought to! From the graphic we can see that Mars is in an orbit about 140 million kilometres outside of Earth’s orbit, but the total distance to travel to intercept Mars is 500 million kilometres. At launch Earth is a bit ‘behind’ Mars as we circle the sun so this will have helped determine the launch date to make sure that there is time for Exo-Mars to slow down from its initial velocity calculated by adding the Earths speed as it moves around the sun of 107,000 km/h to the launch velocity required to escape from the Earth’s gravity of about 48,000 km/h which gives 155,000 km/h. Now Mars is ‘only’ travelling at 86,000 km/h as it moves around the sun so Exo-Mars has obviously got to apply the brakes to reduce its speed to match that of Mars during the 218 days travel time.

The average speed to travel 500 kilometres in 218 days is 96,000 km/h, but this speed is relative to the suns frame of reference, not that of Earth which is how the launch velocity is expressed as this is the vital number to know if an object can escape from Earth’s gravity and reach its intended destination. New Horizons needed a higher initial velocity as it needed sufficient speed to make its first gravity assist rendezvous and continue out beyond the clutches of the suns gravity.

subdirectory_arrow_rightNew Horizons’ record speed of 56,000 km/hr was its speed relative to Earth. Put more literally, this was how quickly Earth and New Horizons were moving away from each other on launch day.

By comparison, the ExoMars probe launched at a speed of about 33,000 km/hr, also relative to Earth. This means that, with each passing hour, ExoMars and Earth are 33,000 kilometers further away from one another. At this rate, it would take under 12 hours for ExoMars to be as far away from Earth as the Moon.

But while ExoMars puts distance between itself and Earth, both objects also travel around the sun at incredible speed: about 108,000 km/hr. It’s a bunch of complicated math to find out how quickly ExoMars is moving relative to our Sun, but it started off moving 108,000 km/hr in the same direction as all of us – and then a Russian rocket changed its trajectory by 33,000 kilometers per hour in a direction that will take it towards Mars.

As ExoMars travels along its new orbit, it’s still moving at around 100,000 km/hr relative to the Sun (but only a few tens of thousands of km/hr relative to Earth). Eventually, this orbit will carry it into the orbital path of Mars, at which point it will fall into orbit around the red planet. In total, ExoMars will travel about 500 million kilometers AROUND the Sun in order to reach Mars, as there is no way to take a direct path in a straight line.

Fun fact: if you factor in the Sun’s relative velocity around the center of our galaxy, you could say that ExoMars is traveling through the Milky Way at well over 500,000 km/hr. It’s all relative to the point from which you make your measurement.

subdirectory_arrow_rightAll its possible if you have enought power resurce because in space dont have frction soo nothing stop that(except impact with another object or the gravity if go close to stars).At launch and orbit on low orbit earth was 27000km/h after that (3days i think was) you get same impulse from earth plus the propulsion satelite. The propulsion if it is constant acceleration you have to plus to the old speed. Expl: earth orbith(27000km/h) + impulse from earth rotation + constant acceleration. The question is who much speed have the spaship when leave earth orbit and who much acceleration per hour can give that motors.

subdirectory_arrow_rightIt says that the exo mars will travel 500 million km in approx 218 days.If we compare this to the mangalyaan (India’s mission) it will travel approx 712 million km in approx 300 or less days.This is clear that this speed of exo mars is possible.

Second point is that the sun’s gravity gives the spacecraft a boost so the speed is not relative to the earth but also depends on the sun.

The speed of exo mars is approx 26 km/sec. And the speed of the spacecraft is reduced at the ultimate point in relation to Mars to be captured by the martian orbit which may be around 5km/sec i suppose.

(Thankyou for the question! Got to know something i didn’t know)