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: