What to Expect When InSight Lands on Mars

Emily LakdawallaNov 12, 2018

If all goes well, anxious space fans on Earth will learn of a successful InSight landing on Mars on Monday, 26 November 2018, at 19:53 UTC. As with all Mars landings, no one who is watching will be able to do anything to affect the outcome; all we can do is wait and hope everything works. JPL shared a great video featuring Mars landing engineer Rob Manning explaining how everything works. Here, I made you an infographic to follow along with the action.

Mars InSight landing infographic
Mars InSight landing infographic Advance predictions for the details of InSight's landing made several weeks beforehand. Adjustments to the trajectories of InSight or Mars Reconnaissance Orbiter may change these times by up to several seconds, as could weather on landing day. All times include 8.1 minutes of one-way light time delay (accounting for the time it takes signals to travel from Mars to Earth). Abbreviations used in the labels: EDL = entry, descent, and landing; E = entry; T = touchdown; h m s = hours, minutes, and seconds; UT = Universal Time (subtract 8 hours for Pacific, 5 for Eastern, add 1 for European time, add 8 for Japan). Revised 15 November 2018 to correct an error in InSight's atmospheric entry speed.Image: Emily Lakdawalla for The Planetary Society

InSight’s will be a throwback landing, simpler than Curiosity’s and identical to Phoenix's. It will employ heat shield, parachute, and landing rockets, but no fancy entry guidance or Skycrane maneuver. Even if it’s simpler, it’s still terrifying, a period during which decades of work comes down to minutes of automated maneuvers that’ll transform a space-faring flying saucer into a sessile lander.

It all unfolds at a world that’s 8.1 minutes away from us by light speed. By the time we on Earth receive a signal that tells us InSight has sensed the atmosphere, it’ll all be over, one way or another, up on Mars. (Those of you who are about to “actually” me about the illusion of simultaneity: please resist the urge.)

From the moment that InSight hits the top of Mars’ atmosphere to the moment that its legs touch the ground, just 6 minutes and 45 seconds will elapse. Long-time observers may notice that this is slightly less than Curiosity’s “7 minutes of terror.” (Actually, Curiosity's landing took a total of 7 minutes and 12 seconds, a fact I just looked up in my book.) There are two reasons InSight’s descent will be a little faster. For one thing, Curiosity used a smart guided-entry system that could steer to level out its flight, adding to its time spent in the atmosphere; InSight’s landing is ballistic. For another, Curiosity landed in a deep hole, a spot more than 1800 meters lower than InSight’s landing site. Curiosity’s landing elevation was 4,501 meters below the Martian mean; the center of Insight’s landing ellipse lies at 2,655 meters below mean. Mars doesn’t have a sea level, so after the Mars Global Surveyor mission measured Mars’ topography, scientists defined zero elevation on Mars as an average planetary radius of 3,396 kilometers. All landing sites have been below this elevation because heat shields and parachutes need as much atmosphere as they can get to slow down incoming spacecraft.

Here is a detailed timeline of the anticipated events at Mars, reproduced in a variety of time zones. All of these times are Earth received time, which means they’ve had 8 minutes 7 seconds added to spacecraft event times to account for how long it will take signals to traverse the space separating Mars from Earth.

EventTime to
Final EDL parameter update-3h08:4711:4716:4717:47
This is the last chance that navigators have to fine-tune InSight's targeting at the top of Mars' atmosphere. They can take into account weather data from Mars Reconnaissance Orbiter, MAVEN, and Curiosity to decide whether to adjust the aim point based upon today's predicted Mars eweather.
NASA TV live coverage starts-1h11:0014:0019:0020:00
Heaters begin preparing landing thrusters for use-1h11:0014:0019:0020:00
You can choose to either watch the commentated NASA TV public feed, or an uninterrupted clean feed either on the NASA TV Media Channel or YouTube.
Cruise stage jettison; telecom to carrier only-0h 13m 45s11:4014:4019:4020:40
The cruise stage held solar panels for electrical power and rockets that InSight used to steer to Mars. It's not designed to survive entry and doesn't have any ability to slow down, so it will break up on entry and its wreckage will land somewhere downrange (east) of InSight. InSight will run on batteries until it can open its solar panels after landing.
Mars Reconnaissance Orbiter AOS-0h 13m 43s11:4014:4019:4020:40
With the cruise stage out of the way, Mars Reconnaissance Orbiter's Electra radio will be able to detect the UHF signals from an antenna on InSight's aeroshell.
Begin turn to entry attitude-0h 13m 15s11:4014:4019:4020:40
The turn will point the heat shield toward Mars' atmosphere.
Complete turn to entry attitude-0h 11m 45s11:4214:4219:4220:42
Begin UHF transmission of landing telemetry-0h 8m 45s11:4514:4519:4520:45
Two MarCOs, Mars Reconnaissance Orbiter, and ground-based telescopes will be listening. (The spacecraft at Mars will have been picking up the signal for 8.1 minutes, according to their clocks, of course.)
Entry interface-0h 6m 45s11:4714:4719:4720:47
Mars' atmosphere doesn't have a sharp boundary. This moment in time and position in space are what InSight was aiming for. Beyond this, Mars' atmosphere will increasingly influence InSight's path.
Peak heating (1500°C)-0h 5m 15s11:4814:4819:4820:48
This is hotter than lava, hot enough to melt steel, but the pulse of heat is brief and it will do no more than char and ablate the outermost layer of the heat shield. Ionized gas spreading around the incoming spacecraft may cause a brief interruption in the ability to detect InSight's radio transmissions.
Peak deceleration (7.5 g)-0h 4m 50s11:4914:4919:4920:49
Friction between the atmosphere and the heat shield will ultimately cancel out 99.5 percent of InSight's kinetic energy, even before the parachute opens.
Begin acquisition of HiRISE image-0h 3m 8s11:5014:5019:5020:50
HiRISE is the high-resolution camera on Mars Reconnaissance Orbiter. It has successfully imaged both Phoenix and Curiosity while they were landing on Mars in order to document the state of the parachute. It will try again with InSight, but the angle is challenging and the image likely to be smeared. It will take about 100 seconds for HiRISE to complete acquiring its long image swath.
Parachute deploy-0h 3m 7s11:5014:5019:5020:50
An explosive sabot shoots the parachute out the back of the aerosell, and it snaps open within 2 seconds.
Heat shield jettison-0h 2m 52s11:5114:5119:5120:51
The heat shield will fall to the surface somewhere downrange (east) of InSight, but not as far downrange as the cruise stage debris.
Lander legs deploy-0h 2m 42s11:5114:5119:5120:51
End acquisition of HiRISE image-0h 1m 28s11:5214:5219:5220:52
If HiRISE's image swath intersected InSight's path while InSight was passing through the swath, we will have a photo of InSight under parachute. The photo will not be downlinked to Earth for at least 2 and as many as 48 hours.
Radar senses surface-0h 1m 0s11:5214:5219:5220:52
Lander separation-0h 0m 45s11:5314:5319:5320:53
The lander will drop like a rock for one second to clear away from the backshell. There may be a brief pause in spacecraft transmission as it switches from the antenna on the backshell to the antenna on the lander. The backshell and parachute will land nearby the lander, uprange (to the west) and somewhat north or south.
Descent engines fire-0h 0m 44s11:5314:5319:5320:53
The landing rockets will counter both horizontal and vertical motion detected with radar. If the lander has sensed that it's not moving very fast horizontally, it will perform a sideways divert maneuver in order to make sure the backshell doesn't fall on it and then work to cancel out the horizontal motion. The spacecraft will also rotate itself to orient its solar panels east and west and its workspace to the south.
Constant velocity descent-0h 0m 15s11:5314:5319:5320:53
The spacecraft will transition to a constant descent speed of 2.4 meters per second until touchdown.
Touchdown+0h 0m 0s11:5314:5319:5320:53
InSight will detect the touchdown, turn off its landing rockets, and change the tone of its carrier signal to indicate that these steps have happened successfully. InSight has a list of activities to do within minutes after landing, including taking the first photos.
Mars Reconnaissance Orbiter LOS+0h 4m 27s11:5814:5819:5820:58
Once Mars Reconnaissance Orbiter gets within about 10 degrees of InSight's horizon, it will lose contact with the lander. Exactly what time this happens depends on where in the ellipse InSight lands, how well the radio keeps contact at low elevations, and whether the lander is tilted.
Solar panel deployment begins+0h 16m 0s12:0915:0920:0921:09
NASA TV live coverage ends+0h 36m 2s12:3015:3020:3021:30
Solar panel deployment complete+0h 32m 0s12:2515:2520:2521:25
InSight waits long enough for dust to settle before opening up the fan-shaped solar panels. This final step is crucial for the survivial of the spacecraft, which has been running on battery power since the separation of the cruise stage.
Post-landing news conference (NET)+2h14:0017:0022:0023:00
Mars Odyssey rise+5h 4m 32s16:5819:5800:5801:58
Mars Odyssey set+5h 21m 12s17:1520:1501:1502:15
Odyssey will receive a UHF transmission from InSight containing all its landing telemetry and possibly (but not definitely) some photos, possibly including ones taken with dust cover off.

How We’ll Follow InSight’s Landing

There are several ways we’ll be able to receive InSight’s radio signals to find out how the spacecraft is doing. Mars Reconnaissance Orbiter will record data for later replay, but there are a few real-time listening methods. None of the real-time methods is as certain to work as the record-and-decode later method -- but we’ll probably get some real-time information, one way or another.

(Note: When I talk about “real-time” here, what I actually mean is “spacecraft time plus the 8.1 minutes it takes radio signals to travel from Mars to Earth.”)

If we’re lucky, the MarCO CubeSats will receive InSight’s radio signal directly, decode it, and retransmit it to Earth using their stronger antennas. This “bent-pipe” relay could give us great detail on the spacecraft’s understanding of its health and the progress of the landing.

MarCO data relay diagram
MarCO data relay diagram MarCO will relay data from InSight to Earth during InSight's descent through Mars' atmosphere and touchdown on the surface.Image: NASA / JPL-Caltech

Even if the MarCOs don’t work, we’ll still have a way to get real-time information. Any radio communication uses a carrier signal at one specific frequency, then wiggles that signal in some way in order to transmit information. It’s easier to detect a carrier signal than it is to detect the little modulations of the signal. The carrier signal from InSight will be detectable from Earth using large radio telescopes (specifically, Green Bank Observatory in West Virginia and the Max Planck Institute for Radio Astronomy’s Effelsberg, Germany facility), but the modulations on top of that carrier signal are too weak to be detected across such a great distance.

What can we learn in real time by detecting InSight’s carrier signal from Earth?

  • As long as InSight’s transmitting, we know it’s alive and not crashed or burned up. The inverse is not true, however. In fact, there are two moments when we actually expect to lose signal even if InSight is perfectly healthy. One is during “peak heating” on entry, when ionized gases around InSight may interfere with the radio signal. The other is after the lander separates from the backshell, when it will switch antennas from one mounted on the backshell to one mounted on the lander.
  • Doppler shifts in the frequency of the carrier signal provide a sensitive measure of how fast the spacecraft is traveling. Navigators will compare this speed to predictions to assess whether the landing is taking place as predicted. Sharp changes in speed can tell us when the lander has hit the atmosphere and when its parachute opens, even though we’re not able to hear the spacecraft specifically telling us these things.
  • InSight’s legs contain trigger sensors that will shut off the lander rockets when they detect touchdown. When the sensors trigger, InSight will shift the frequency of its carrier signal to a slightly different one, indicating detection of the surface. Earth-based telescopes will be able to detect that change in carrier signal frequency. (Note, however, that touchdown detection does not necessarily mean the spacecraft is in a safe state.)
  • If the predicted landing time passes and InSight is still communicating with us, that’s strong evidence that it survived the landing in good working order!

So while I’d like the MarCO satellites to work, and I hope they work, I know we’ll get enough information to follow even if the MarCO connection doesn’t work. Assuming, of course, that everything on InSight works as planned!

When Will We Get the First Images?

The short answer: The first image could arrive as early as 10 minutes after landing (so, about 20:05 UT or 12:05 PST), but possibly as late as 20 hours after landing.

There are two cameras on InSight, one (the Instrument Context Camera, or ICC) designed to view the workspace in front of the lander, and one (the Instrument Deployment Camera, or IDC) attached to the arm. Within minutes after landing, the workspace camera will take a photo. The lens cover will still be on, so the photo will be covered with dust blotches from the stuff kicked up during landing. An hour-ish later, some time after the solar panels have been deployed and the lens cover opened, the same camera will take another photo. (This much was confirmed for me by JPL Public Affairs.) If history is any guide, the first image to be returned will be a thumbnail of the lens-covered one at a quarter of the original resolution, a little file 256 pixels square. It’s not a lot of data, but it’s lower-priority than other kinds of data that the spacecraft will be sending to Earth, so mission managers can’t be certain it’ll get transmitted right away.

The landing press kit does a great job explaining the uncertainty around how and when we’ll receive that first picture, so I’m just going to copy and paste all that text here:

Once InSight has touched down on the Martian surface, there are several opportunities for the lander to send back an image from the Martian surface. The cameras will have their covers on for each of these opportunities, which could obscure the images slightly. (The first images from the Curiosity rover included its dust cover.)

The lander has been programmed to take its first images several minutes after touchdown. The transmission of these images back to Earth will take longer. Engineering data are prioritized above images so it’s possible that only part of an image (or none at all) will be transmitted in the first hours after landing. The image could be transmitted at various times via MarCO, MRO or Odyssey.

How InSight’s First Images Could Be Returned to Earth:

  • MarCO, the experimental pair of CubeSats, could relay back a first image just after the entry, descent and landing phase. If this happens, the image (or partial image) could be available within 10 to 20 minutes of touchdown.
  • MRO could -- but is unlikely to -- relay back an image. MRO will prioritize relaying engineering data as it is setting over the Martian horizon. An image received via MRO wouldn’t be ready until late afternoon.
  • Odyssey could -- but is also unlikely to -- relay back images during its first pass, which occurs several hours after InSight lands. At that time, it will receive a recording of the EDL data from InSight. It may not be able to transmit image data before it passes over the horizon; if it did, it would be available in the early evening.
  • Odyssey will also pass over InSight the day after landing between 6 and 8 a.m. PST (9 and 11 a.m. EST) [14:00 and 16:00 UTC] on Nov. 27.

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