Thread by @elakdawalla

Join me LIVE Feb 18 with @VICENews at 11:45 PT / 14:45 ET / 19:45 UT to witness the landing of @NASAPersevere! I'll share all the detail I can cram into my brain over the next 2 days -- technical geekery you won't get on any other public broadcast.

Before landing I'll have 2 guests. First up will be @LifeAtPurdue's Briony Horgan to talk about @NASAPersevere's science mission eaps.purdue.edu/people/profile…

My second guest on the Feb 18 @VICENews livestream will be @NASAJPL's @YazzieSays says, to talk about @NASAPersevere mechanical engineering, especially the sample-collection plans! aaronyazzie.com/about

But then once the critical landing events get underway, it'll just be you and me and the *uncommentated,* clean media feed out of @NASAJPL -- I'll shut up when anybody from mission control is speaking, and then I'll repeat and translate in the dead time between announcements.

Most of the Perseverance landing technology is copied over from Curiosity. I explained all of that in my book, "The Design and Engineering of Curiosity." It's only $26 from Amazon today. If you want an electronic copy, buy that direct from Springer-Praxis. amzn.to/37o4VEl

I just posted an updated @NASAPersevere landing event timeline with the most up-to-date info from @nasa_eyes. Download the Excel version from my Patreon, change the "local time offset" number to your local time offset from UTC, and get your local times. patreon.com/posts/47717229

(I am freelance now. Patreon is one way I support myself to continue doing this work. Please consider supporting me there. Thank you!)

An explainer on the time columns: there is 11+ minutes of light-time delay between Earth and Mars today. The rover has its own clock, counting up Spacecraft Event Time (SCET). Its events happen according to that clock. >

We learn about the events that happened on Mars 11+ minutes later. This is Earth Received Time (ERT). On top of that, Earth has time zones. Mission time is counted according to Universal Time, UTC. Right now that is the same as GMT. Here in California, my clock is UTC-8. >

When the mission announcers talk about "now" today, they are talking about Earth Received Time. Events already unfolded on Mars 11+ minutes before that, but it's "now" in a timey wimey, Jeremy Bearimy kind of way. I try not to think too hard about that and just go with the Now.

How does all that Mars-to-Earth telecom work? There are 2 ways we receive data. One is Direct-To-Earth (DTE), from rover antennas, picked up by Deep Space Network stations. Today Madrid will be prime, with Goldstone serving as backup. Data rates are low. >

The spacecraft has a series of predefined "tones" or frequencies it broadcasts direct to Earth as signals -- one for "I ejected the cruise balance masses!" another for "I deployed my parachute!" and so on. Plus, Doppler tracking tells us velocity change very precisely. >

Direct-to-Earth only works if spacecraft can see Earth. 2 minutes before landing, Perseverance will go over the horizon as seen from Earth -- DTE transmission will be lost. This is right around parachute & Terrain Relative Navigation phase, which is a bit scary! but planned.

Second data transmission is from spacecraft UHF antenna, to Mars Reconnaissance Orbiter, which quickly decodes data and then sends it to Earth. This is "bent-pipe" relay and will work even after loss of DTE, we hope. In fact, if it works, we should get images upon landing. >

Finally, MAVEN will also be listening. It will not be relaying to Earth. Instead, it will record raw, undecoded UHF transmissions from Perseverance and send them to Earth after all is over. If today is a very bad day, it will be MAVEN's recordings that help us understand why.

There will be 2 final telecom opportunities on Perseverance sol 0: Mars Odyssey at about 4.5 hours after landing, and ESA's ExoMars Trace Gas Orbiter about 6.5 hours after landing should get us MUCH BETTER IMAGES if everything goes well.

And maybe we'll even get another amazing Mars Reconnaissance Orbiter HiRISE photo of a Mars lander under parachute. It is definitely going to try to shoot a picture -- cross your fingers that they catch it!

I'm signing off of Twitter now until after the livestream is over. Friends and family who have my cell phone number, feel free to text me questions -- I'll try to answer if I can during the broadcast. Go Perseverance!