Why Is It So Difficult To Send A Spacecraft To Mars?

Artist's conception of InSight space craft landing on Mars yesterday,

Analysis diagram for the trajectory of a spacecraft with respect to the Sun and arrival point at planet (say Mars), with arrival velocity U _A , hyperbolic excess  velocity v _A  and final velocity vector V _A  .  The quantities with subscript 'D' refer to departure values, i.e. from Earth  (at which V_D   denotes the initial velocity vector)


Simplified trajectory for spacecraft to get to Mars.  The '300 million mile' distance cited for Insight refers to the total distance of the curved path.


Contrary to what we've read in some recent media pieces (e.g. Denver Post, Sunday, p. 13 A)  Mars is not "relatively easy to get to". It remains damned difficult, and if a team hasn't got its wits about it, all i's  dotted and  t's crossed, the trip can end up in a scientific dumpster. Say like the time two teams diverged on the units for critical parameters for the Mars Climate Orbiter,  e.g.

http://www.cnn.com/TECH/space/9909/30/mars.metric.02/

Things went very wrong, very fast. In the case cited,  NASA lost a $125 million orbiter because a Lockheed Martin engineering team used English units of measurement while the space agency's team used the more standard (and internationally accepted)  metric system for a key spacecraft operation.  This mismatch in units wrecked the 286 -day mission though assorted space heads declared that QA ought to have caught the problem in advance. Well maybe, but maybe not.

The stat which escapes too many, however, is that only about 40 percent of Earth- launched spacecraft have successfully landed on Mars.  The problems begin with one of the most difficult problems in astrodynamics, the restricted  three body problem. That is, the launching of a relatively small space craft (say like the Mars InSight) from one planet (Earth) to a destination planet (Mars). 

The interplanetary trajectory shown - under the artists' conception of the InSight landing -  conveys the basic details, but in radically simplified form.  Thus, we consider that given a specific a date of departure (T _D )  from planet D (Earth) and the date of arrival (T _A ) at planet A (Mars) we can compute a conic trajectory between planet D and planet A - provided we assume the two planets to be massless. (There is the great simplification!  The actual working using mass values  is obviously much more difficult!) 

The "conic solution" (see diagram)  aspect is one I've discussed in previous posts, e.g. from Feb. 16, 2017:

Brane Space: Analytic Geometry Conclusion: G

eneralizing 2nd …

The ephemerides of each planet (i.e. their orbital parameters at specific times) are given as a function of date so we can obtain the position vectors ( R _D   and   R _A ) and the  respective velocities with respect to the Sun ( U _D   and   U _A  ) of the two planets at the dates.    The next step would be to compute the position vectors and the flight time, D  t , i.e. between the dates  T _D  and  T _A .  The applicable solution then yields the initial and final velocities, V _D   and   V _A in a heliocentric (Sun-centered) coordinate system.  Then the velocity vectors with respect to the departure and arrival planets can be obtained:

i)  v _D   =  V _D     -    U _D

ii) v _A   =  V _A     -    U _A


The subjects of each of the above equations are known as the v-infinity or 'hyperbolic excess velocity vectors'. The value v _A  is critical as the craft approaches the arrival.  Alas, here is where the oft quoted "seven minutes of terror" comes in- about which the media (correctly) makes so much ado. The reason?  There is a perturbation owing to the planet's (Mars') mass which causes an instantaneous velocity change.   How is this critical? Well, given the InSight craft needed to brake from 12,500 mph to 5 mph one can understand why.

The braking alone, never mind reaching velocity  v _A    near Mars,  means the heat shield must survive the entry into Mars' atmosphere, and a supersonic parachute must properly deploy to get help  the landing velocity to 5 mph.  Hundreds of things can go awry in the transit, make no mistake.  (The deceleration to landing speed is also helped by a dozen rocket thrusters and shock-absorbing landing gear.    The landing sequence is also done on automatic pilot because command signals from Earth would take too long.)

For precision work, just to get to the velocity v _A   one must solve the problem using one or other perturbation methods. (One method entails using a planetary gravitational potential function with Legendre polynomials, e.g.

http://brane-space.blogspot.com/2010/07/another-special-function-legendre.html


Given all the mathematical hurdles which had to be conquered (for which I've barely touched the surface)it's little wonder cheers erupted  at the Jet Propulsion Laboratory in Pasadena, , which operates the spacecraft.  This transpired  when InSight sent back an electronic acknowledgment of its safe arrival on Mars. As the press accounts portrayed, "that was the end of a journey of more than six months and 300 million miles."

Jim Bridenstine, the NASA administrator, was in the control room listening as each milestone of the landing process was called out, each followed by a round of clapping, expressed the view of most of the engineers on NASA TV:

 “It was intense, and you could feel the emotion.”

In the months ahead, InSight will begin its study of the Martian underworld, with the aim of helping scientists understand how the planet formed, lessons that could help also shed light on Earth’s origins. It will listen for tremors — "marsquakes" — and collect data that will be pieced together in a map of the interior of the planet.  Ultimately, astronomers hope that by studying the deep interior of Mars insight will be forged into the processes that shaped the other inner planets of the solar system - including Mercury, Venus and Earth - more than 4 billion years ago.

InSight landed at Elysium Planitia, near the Martian Equator in the northern hemisphere. Mission scientists have described the region as resembling a parking lot or “Kansas without the corn.” Within minutes, the first photograph from InSight appeared on the screen, eliciting another round of cheers.


See also:

https://www.theguardian.com/science/2018/nov/26/nasas-mars-insight-probe-touches-down-on-mars

And:

https://www.youtube.com/watch?v=05eLnSQCNVg

A 16-month Flyby Trip to Mars? NO Thanks!

Mars as it might appear during flyby on August 20, 2018 for the 'Inspiration Mars' couple, before heading back to Earth. (From European Space Agency)

According to a story in yesterday’s Denver Post (‘16-Month Trek to Mars and Back would Test Couple’s Marital Arts’, p. 2B) a consortium of private space specialists- backed by a tycoon- plans to send a ‘bare bones’ mission to Mars in five years. It will be a “no frills” 16 month flyby journey that will feature a husband and wife team, given such would more likely be able to handle being cooped up for well over a year in a cabin half the size of an RV.


The private, non-profit project is being called “Inspiration Mars” with the initial front money coming from multi-millionaire investment consultant Dennis Tito (The first ever space tourist, i.e. aboard a Russian Soyuz craft). The cost estimate? About $1 billion. NASA will not be involved. Instead the private backers plan to use a private rocket (they don’t elaborate, but it would have to have at least the power of a Saturn V). They insist they can get the couple to Mars at less than half the cost that NASA could.

Pardon me if I don’t buy it. Even given such a bare bones project (e.g. they will recycle urine as drinking water) the cost to construct a survivable craft for a 16 -month mission will be at least double the cost of the  first Apollo Moon mission (11) in today's dollars, or about $3.5b. It is simply impossible to do it for less and not make it a suicide mission. You are after all, traveling through regions of interplanetary space likely to be filled with meteoroids, and even micro-meteroids. The latter could easily put a hole into the craft and if there aren’t redundant systems available or a ‘skin’ built to survive puncture, the occupants will perish in their first such encounter. What will $1b get you? Well, a very cheap robot mission!


Would I want to make such a trip? Hell no! At least not from any private, untested craft. (Obviously, doing all the appropriate testing first will bring the costs up majorly!)


Which is why the privateers admit it is a “huge risk” and much more than a government agency like NASA would be prepared to take. (Imagine the PR problem if a Class X solar flare erupts while the craft is en route and the occupants are killed by the high intensity radiation, especially because shielding wasn't given priority in a "bare bones" project.)


Some have compared it to the Apollo 8 flyby of the Moon in December, 2008, but that was a three day trip there and  three days back, covering a quarter million miles each way. Meanwhile, the planned Mars mission will cover 150 million miles and take 501 days overall. While the Apollo 8 crew actually orbited the Moon for 20 hours before returning, the Mars couple will only do a brief Mars "flyby" (since their trajectory is based on the 'sling shot' effect'), lasting maybe an hour if that, before proceeding on their long voyage home. In other words enduring 500 -plus days of cooped up journey time for a reward of only about an hour of actually seeing the Red Planet, and that from a spacecraft a hundred miles up! Pardon me, but that's too little payoff or return for too much time investment!


The project timeline calls for a launch on January 5, 2018, and a Mars flyby on August 20 the same year. The passengers are to return to Earth by May 21, 2019.


NASA spokesman David Seitzman meanwhile has acclaimed the venture as “validating President Obama’s decision to rely more on the private sector.”

Maybe. But I will wait to see whether the proposed Mars mission is actually a success! And by success I mean both occupants landing safe and sound, along with the craft intact.

Can Mars Curiosity Rover Get It Done?

Image of the Mars Curiosity Rover, set to land tonight on the Red Planet

After millions of miles traveling from Earth, $2.5 billion in costs (still barely a quarter of what the Afghan Occupation costs us each month), and five years planning to find the ideal site - the Mars Science Laboratory (nicknamed 'Curiosity') is slated for touchdown on Mars sometime this evening.

Ironically, the tension will arrive not from the long flight itself, but during the final approach, starting from an altitude of roughly 10 km (6 miles) when the two metric ton (2,000 lb. ) spacecraft deploys a parachute 50m (150') long and 21.5 m in diameter to begin its descent to the Martian surface.  This is critical because designing the chute was no easy task and even the experts (if honest) will admit that "the physics of how a parachute inflates at supersonic speeds is not well understood and extremely difficult to model" (Scientific American, July, 2012, p. 41).

Having descended to an altitude of 2 km (1.2 miles) the craft will be traveling at nearly 100 meters a second (330 ft/ sec) and that's using the parachute. This "terminal velocity" is the slowest the thin Martian atmosphere can brake an incoming spacecraft but still much too fast for a safe landing. Hence, this is the most critical point: the stage at which the craft needs to "drop  out" from the parachute and when a rocket powered backpack fires thrusters in the skyward direction, to slow its descent - ultimately to ~ 20 m/ sec. If at any time during this critical phase either the rover fails to separate enough from the chute or the thrusters fail to fire, it will be all over before it even starts. You will then read tomorrow morning or see tonight the news of a crash landing at 100 m/s.

Even this isn't enough for a slow enough landing to retain the delicate equipment, so in addition to the reverse thrusters, three cables will emerge (the "sky crane" so-called, at a height of about 20 m)  on which the rover will be gradually lowered. The end result (hopefully!) will be a "soft"  landing at 0.75 m/sec with wheels and suspension fully deployed. (But note even at this 'slow' speed, the momentum just before impact will exceed 700 kg m/s)  Meanwhile, the powered thrusters package will crash land roughly 450 m away.

It doesn't take a lot to see that failure could occur at any of these critical steps on the final approach to Mars. Needless to say, if even a minor failure occurs (say the suspension and wheels failing to deploy) NASA will have 'egg' all over its collective face, particularly as it elected to eschew working with the European Space Agency (ESA) to send collaborative missions in 2016 and 2018, opting to go it alone. The risks are enormous given the agency is eyeing further exploration of the Red Planet, and any kind of disaster would have serious repercussions in the eyes of the budget cutters. This will be especially so if the  Repugs get in power in November, and grab all branches of government.

Curiosity itself is the most technologically advanced craft ever - of the 6 to successfully land on Mars - out of the 14 total attempts made by all Mars-faring nations. The Rover (see image, compliments of NASA) is nuclear -powered and equipped with more than a dozen high tech cameras, a weather station and tools to drill, and 'sniff' the environment in search of life. Perhaps the neatest instrument is a laser-induced breakdown spectrometer which can zap holes in rocks and soil up to 7 m (21 ft.) away and remote sense their chemical composition.

The "rudimentary life form" optimists at NASA are keenly awaiting such tests, along with those from the 'SAM' or sample analysis device, because they believe the pre-selected landing site (Gale Crater) merits it.  Of 50 original candidates this was the one finally chosen based on a number of factors: including the exposure of ancient river deposits compliments of wind erosion over the ages, and mineral-rich terrain analogous to those on Earth which lie near groundwater aquifers. My own view is that despite all the shiny new toys, no life will be found - even microbial single-celled life. I simply don't believe any life exists on Mars, if it ever did.

Within an hour of its successful landing the Curiosity rover will commence its work, mainly getting some terrific imagery of the surface. Within another month and certainly by the end of the 2nd, barring mishaps, the onboard lab will have analyzed the first rock and soil samples.

Let us hope, for NASA's sake, and that of future exploration (including manned, since we can't stay on this one world forever) that this latest Martian endeavor turns out to be as big a success as its purveyors and creators are now hyping!