Seven Minutes of Terror

NASA Mars InSight landingNASA’s Mars InSight lander is now approaching the Red Planet and will attempt to land later today.  Here is a timeline of events during the entry, descent, and landing (EDL) phase if everything goes as planned (adapted from the NASA/JPL “Landing Milestones” page).  All times are in Universal Time (UTC), which you can see in the title bar at the top of the Ratburger page.

  • 19:40 UTC – Separation from the cruise stage that carried the mission to Mars
  • 19:41 UTC – Turn to orient the spacecraft properly for atmospheric entry
  • 19:47 UTC – Atmospheric entry at about 19,800 kilometres per hour, beginning the entry, descent and landing phase
  • 19:49 a.m.UTC – Peak heating of the protective heat shield reaches about 1,500 °C
  • 15 seconds later – Peak deceleration, with the intense heating causing possible temporary dropouts in radio signals
  • 19:51 UTC – Parachute deployment
  • 15 seconds later – Separation from the heat shield
  • 10 seconds later – Deployment of the lander’s three legs
  • 19:52 UTC- Activation of the radar that will sense the distance to the ground
  • 19:53 UTC – First acquisition of the radar signal
  • 20 seconds later – Separation from the back shell and parachute
  • 0.5 second later – The retrorockets, or descent engines, begin firing
  • 2.5 seconds later – Start of the “gravity turn” to get the lander into the proper orientation for landing
  • 22 seconds later – InSight begins slowing to a constant velocity (from 27 km/h to a constant 8 km/h) for its soft landing
  • 19:54 UTC – Expected touchdown on the surface of Mars
  • 20:01 UTC- “Beep” from InSight’s X-band radio directly back to Earth, indicating InSight is alive and functioning on the surface of Mars
  • No earlier than 20:04 UTC, but possibly the next day – First image from InSight on the surface of Mars

Here is a description of the entry, descent, and landing phase.

You can watch live coverage of InSight’s arrival at Mars starting at 18:30 UTC on:

Here is the Landing Day – 1 press briefing.

Two CubeSats called MarCO-A and B are shadowing InSight’s path.  They are the first CubeSats launched on an interplanetary trajectory.  If successful, they will provide a real-time communications link between the lander and Earth.  They are not, however, required for a successful landing.  If they fail, information on the landing may be delayed until it can be relayed by another spacecraft orbiting Mars.  After doing their job, the MarCO CubeSats will fly by Mars and continue to orbit the Sun for billions of years, just like Elon Musk’s roadster.  Here is a video about the MarCO mission.

Here are more details about MarCO.

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Author: John Walker

Founder of Ratburger.org, Autodesk, Inc., and Marinchip Systems. Author of The Hacker's Diet. Creator of www.fourmilab.ch.

21 thoughts on “Seven Minutes of Terror”

  1. Looking at the landing timeline, you might wonder why they deploy a parachute and then, a little over two minutes later, cut it away and discard it, then use rockets to land.

    Landing on Mars is particularly difficult because while it has around 1/3 the Earth’s gravity, its atmosphere is only 0.6% as dense.  (As on Earth, atmospheric pressure varies with altitude and since on Mars most of the northern hemisphere is lower than the highlands of the southern hemisphere, that’s where most landing missions have been sent, since it’s easier to land there because you have a denser atmosphere to help dissipate energy.)  Upon arrival at Mars, the heat shield is used to brake from the arrival speed of 5500 metres per second (as a fan of Kerbal Space Program, I find it more natural to think in metres/second than NASA’s per hour units) to around 380 metres/second.  This dissipates around 90% of the initial kinetic energy at atmospheric entry.  However, this is still supersonic, and at this point there isn’t enough atmosphere or altitude left to brake much more with the heat shield.

    This is where the parachute is deployed.  It is a special design which allows it to open at supersonic speed in Mars’s thin atmosphere, and it dissipates around 90% of the remaining kinetic energy of the lander.  However, because the atmosphere so thin, it is still moving far too fast to survive landing.  A parachute which could slow the lander to a safe speed would be much too large and heavy to be practical, and getting it to deploy in the time remaining before impact would be very difficult.

    So, the solution is to cut away the parachute (actually accomplished by having the lander drop away from the backshell to which the parachute is attached) and fire its retro-rockets to cancel most of the remaining velocity.  After detecting the surface with its landing radar, it throttles its engines to touch down at around 2.2 metres/second (which is still pretty fast if you’re doing it yourself: it’s like driving your car into a wall at five miles per hour).

    This is explained in the Landing Day – 1 press briefing video in the main post starting at the 14:00 point.

    Earth’s dense atmosphere allows the heat shield alone to slow a spacecraft to the point a subsonic drogue parachute can be deployed which further slows it and pulls out the main parachute(s), which can slow the lander to a safe speed.  The easiest place to land in the solar system is Saturn’s moon Titan, whose surface gravity is just 14% of Earth’s but has an atmosphere 1.45 times denser than that of Earth.  Only one landing mission has been sent to Titan, and it succeeded on the first try.  Here is recently-reprocessed imagery from the landing on Titan.

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  2. Richard Easton:
    Sorry John for the simplistic question but I haven’t been following this.  How does the  InSight rover compare to Curiosity.

    InSight is not a rover, but a much smaller and lighter lander which does all of its science at the location where it lands.  Its focus is on investigating the internal structure of Mars, and that can be done anywhere on the planet and does not require moving around.  Its principal instruments are the Seismic Experiment for Interior Structure (SEIS), a highly sensitive seismometer capable of detecting marsquakes anywhere on the planet and using them to map internal structure, and the Heat Flow and Physical Properties Package, which will use a “mole” to burrow 5 metres beneath the surface and deploy a chain of heat sensors to measure heat flow from Mars’s interior to the surface.

    The entire science payload is just 50 kg, compared to the Curiosity rover which weighs 899 kg.  InSight carries only two rudimentary cameras for engineering purposes and to choose a location to place its instruments on the surface, while Curiosity carries 17 different cameras of of five types.

    Because InSight can do its science anywhere, it was targeted at Elysium Planitia, “the most boring place on Mars”, because it is least likely to encounter terrain or rocks which might interfere with landing or deploying its instruments there.

    This is the first time a seismometer has been sent to Mars since the Viking landers in 1976.  The Viking seismometers failed to detect any marsquakes because they were mounted to the body of the lander and were disturbed by motion of lander components and the wind.  The InSight seismometer will be placed directly on the surface by a robot arm, with a flex cable connecting it to the lander, and then a wind and thermal shield will be deployed around it.  It is also far more sensitive than the Viking instruments.

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  3. John Walker:
    After doing their job, the MarCO CubeSats will fly by Mars and continue to orbit the Sun for billions of years, just like Elon Musk’s roadster.

    John Walker:
    The easiest place to land in the solar system is Saturn’s moon Titan, whose surface gravity is just 14% of Earth’s but has an atmosphere 1.45 times denser than that of Earth.

    Perhaps Musk should have tried to land the roadster on Titan.

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  4. InSight has landed safely on Mars.  The first image from the surface has been received.

    Mars InSight: First image from Mars

    The “safe landing” X-band beep has been received.

    The image shows the sky, horizon, and terrain.  It is obscured by debris from the landing deposited on the transparent lens cap.  The lens cap will be jettisoned after waiting for all the dust to settle, permitting clearer images to be taken.  The camera has a fisheye lens, which results in the curvature of the horizon near the top.

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  5. Here is a version of InSight’s first image, manually retouched by Jason Major of JPL to remove the lens cap debris and some of the barrel distortion.  This is not what the camera saw, but a reconstruction.

    Mars InSight first image, retouched

    First images are more about “Hey!  I’m here and the camera works!” than science.  Below is the first image from the surface of Mars taken by the Viking 1 lander on 1976-07-20.  I watched this image come in line-by-line in the Caltech auditorium while I was working as a consultant at JPL to support their Univac mainframe computers during the first Viking landing.

    Viking 1 lander: first image from Mars

    The InSight mission isn’t about photography, so don’t expect any spectacular photos of the “best parking lot on Mars”.  Its cameras are basically of GoPro quality, although radiation hardened and space qualified.  It will probably be two years before the scientific results based on marsquake and asteroid impacts become clear.  One of the biggest unknowns is how often these events happen.  This is the first time there’s been seismometer on Mars capable of detecting them.

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  6. Gerry D:

    ctlaw:
    Perhaps Musk should have tried to land the roadster on Titan.

    Easier to find a parking place than New York city I’ll bet. And no meter maids!

    And hydrocarbons everywhere to fill up!  Oh, wait—it’s electric—no chargers!  Dooooh!

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  7. MJBubba:

    10 Cents:
    How long will this probe function?

    Just to be obnoxious, does anyone know if NASA filed a Environmental Impact Statement?

    Yes:

    https://planetaryprotection.nasa.gov/overview

    From that page:

    Agreements regarding planetary protection stem from the 1967 United Nations Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Bodies, which states that all countries party to the treaty “shall pursue studies of outer space, including the moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination.” 

    So Matt Damon is an interplanetary criminal and we have video proof.

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  8. ctlaw:
    So Matt Damon is an interplanetary criminal and we have video proof.

    By his own admission, he’s “Mark Watney: Space Pirate”!

    I’ve been thinking about laws on Mars. There’s an international treaty saying that no country can lay claim to anything that’s not on Earth. By another treaty if you’re not in any country’s territory, maritime law applies. So Mars is international waters. Now, NASA is an American non-military organization, it owns the Hab. But the second I walk outside I’m in international waters. So Here’s the cool part. I’m about to leave for the Schiaparelli Crater where I’m going to commandeer the Ares IV lander. Nobody explicitly gave me permission to do this, and they can’t until I’m on board the Ares IV. So I’m going to be taking a craft over in international waters without permission, which by definition… makes me a pirate. Mark Watney: Space Pirate.

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  9. The InSight lander has now returned its second picture from the surface.

    Mars InSight: second picture from the surface

    This was taken by the Instrument Deployment Camera (IDC) located on the robot arm, which has not yet been deployed, so the picture is largely of the arm itself and other equipment on the top deck of the lander, although you can see the surface and horizon beyond the lander.  This is a different camera than the Instrument Context Camera (ICC) which returned the first image shown above in comments #7 and #8.  The IDC, on the arm, was better shielded from dust thrown up in the landing than the ICC which is located on the side of the lander and looks down, so even though the lens shield is still on the IDC, the view is much clearer than yesterday’s image.  This image was relayed to Earth by the Mars Odyssey spacecraft in orbit around Mars.

    InSight has also reported its solar panels deployed and generating electricity and the meteorological instruments and magnetometer are operating normally.  It is expected to take around three months to deploy, calibrate, and commission the seismometer and heat flow experiments before they begin to take science data.

    Meanwhile, an annotated version of yesterday’s first image is today’s Astronomy Picture of the Day.

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  10. 10 Cents:
    How long will this probe function?

    The nominal, funded mission is for two years starting from the landing date.  As the lander is solar powered, was landed near the equator where it receives maximum sunlight and fewer extremes of cold compared to higher latitudes, and the instruments have no complex moving parts, it is likely the lander will continue to function well beyond the primary mission.  The Opportunity rover, which is far more complicated mechanically, continued to operate for fourteen years beyond the end of its nominal 90 day mission, and only died (apparently) this year during a severe planet-wide dust storm.  As InSight is likely to be the only seismometer operating on Mars for quite some time, it is likely an extended mission with a reduced budget and staff will be approved to continue to take data from the seismometer after the end of the planned two year mission.

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  11. Around fifteen minutes after InSight’s landing, the MarCO-B CubeSat, its job of relaying communications from InSight complete, turned around and aimed its camera at the receding disc of Mars.

    MarCO-B CubeSat image of Mars

    This image was taken at a distance of around 7500 km from Mars.  At the right, the high gain antenna used to communicate with Earth is visible.  This is basically a mobile phone camera, so don’t expect a lot of detail.

    Here is a a video from Scott Manley about planetary photography with a smartphone camera.

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  12. John Walker:
    Here is a video from Scott Manley about planetary photography with a smartphone camera.

    The Chinese are going to Mars in two years. It would be interesting if Huawei sent an actual smart phone. They could add a large external lens.

    One obvious problem is that the phone would be out of date by the time it reached Mars. But they could gain some initial publicity by taking photos of earth.

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  13. Mars Insight has now deployed its seismometer on the surface of Mars, nudged it to better connect with the surface, and lowered the wind shield and thermal insulation cover on top of it.  After calibration, it will be ready to return data on Marsquakes.

    Ongoing coverage of the mission, including videos of the seismometer deployment can be found at the mission’s Twitter feed, @NASAInSight.

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