What is the LOWEST orbit for satellites?

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[thrakiamaria]

I am happy that you use metric system for the description of the video.

[nfineon]

No, we haven't explored every corner of our solar system, that would be like saying we visited 8-9 landmarks under the ocean thus have explored every corner of the seas. There's a LOT of space out there and all our satellites have only traversed a tiny fraction of the total area that encompasses our solar system, but yes we've visited most of the major landmarks, not all the moon's yet, nor the belts, ort clouds or intergalactic visitors (omuamua).

[alphaadhito]

Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) operated by ESA orbit at around 250 km and to do so, they had ion thruster continuously firing to maintain that extreme low altitude. Although some satellites and spacecraft had been orbiting as low as below 150 km, they only doing it briefly. Cheers : )

[Snookynibbles]

Nano-satellites, and they are an intriguing trend. Nono satellites represent are small m, as small as a cube a few inches square. Nations line Japan have been launching these; they are primarily research satellites. The advantage is the lower cost not just to produce them, but also the lower cost to put them into orbit. Because nanos are so small, they incur less aerodynamic drag at their very low orbits. Akso, there are now electronic propulsion systems capable of boosting nano-satellites to maintain minimal orbiting parameters.
Separately, lowest satellite orbit ever was achieved by larger tyke satellite that skimmed the Earth with an 80 mile perigee while having a much larger apogee (elliptical orbit). It completed one revolution around the Earth before reentry.

[Snookynibbles]

The 2017, Super Low Altitude Test Satellite (SLATS) or Tsubame using Ion engine propulsion has demonstrated a sustained orbit of 167 kilometers or about 104 miles for a duration of one week.

[environmentNow]

Communication satellites fly that high in order to stay in a geocentric orbit (23h, 56min, 4sec) in order to stay anove the same place in the earth, so people on the groud would have constant communication without changing the dish's orientation (for example satellite TV)

[RWBHere]

GOCE flew at the edge of the atmosphere, and was kept in orbit by an ion thruster. To quote the ESA website, 'Launched on 17 March 2009, ESA's Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission was the first Earth Explorer mission in orbit.' GOCE operated until late October 2013, when its fuel was exhausted, and it de-orbited on 11th November 2013. The craft was somewhat streamlined to reduce the effects of atmospheric drag. There are plans for another launch. You might want to make a video about this interesting satellite.

[johnholleran]

I recently read a study proposing something like 54 km as the new boarder to space. The reasoning is, according to the person conducting the study, that is the statistically lowest altitude a satellite can still orbit before fully reentering. He said there were a few examples of satellites reentering that did at least two full orbits at that altitude, but I don't think that constitutes a better definition to the edge of space. Food for thought. Anyway, thanks for the video, and keep up the good work!

[PaulBalanescu]

Van Allen said 'NOPE' to moonlanding...

[Bitterrootbackroads]

I spend time watching ISS passes, have seen many Starlink trains, and always looking for other satellites. I’ve wondered about lowest possible orbits since witnessing a dim satellite moving west to east at an apparent speed I’m guessing was 4-6 times faster than ISS passes. No idea if it was something in a stable orbit, or if it was something destined to re-enter shortly. If it was in an eccentric orbit, and seen at perigee, it could have been quite low so apparent speed would appear much faster. Do you have any examples of things that can be seen demonstrating very low altitudes?

Assuming a near circular orbit, it seems one could calculate a satellites altitude by by rigging a movable fixture / framework with a couple glow in the dark strings stretched across it, parallel and at a distance from ones eye that can remain fixed. Measure the time it takes for ISS to cross between strings, check time for others to do the same, and do a little math.

[chuckmaster]

The Karmen line is simply the point at which there isn't enough air to provide useful lift to an aircraft in order to stay up. At that altitude, your horizontal speed has to be so high (from the thrust of your engines) that wings don't make a difference any more.

[MarcAus]

I should point out that the hubble telescope is a distant cousin to the KH-11 keyhole satellites, being designed and built by the same companies between the late 80's and 90;s, the hubble of course was optimized for looking outwards, with larger instrument bay and was made to be serviced. It still features the same basic design and 2.4 meter telescope. You may not have heard but the national reconnaissance office gifted a pair of unneeded keyholes (minus the CCDs and classified electronics) to NASA in 2012. These 'obsolete' observatories were made much later than the hubble and are somewhat more advanced, despite still having the same 2.4 meter aperture they have a secondary mirror allowing wider field of view as well as more focused zoom. Fitted with more modern scientific equipment they should be vastly superior to the hubble, especially if launched as a pair for stereoscopic observation. Though NASA probably doesn't have the budget for this. The WFIRST sattelite is planned using one of these satellites, as long as funding doesn't get cut it should launch in a few years.

[klosskopfder.]

there is research by ESA to collect the left air particles, decelerate them and use as fuel of Ion drives. Unfortunately I have no Idea at what altitudes they aim

[dr-syfs]

Wouldn't it make sense for low earth orbit satellites to be streamlined to lower their drag coefficient?

[illya_od_ua]

Spy secret satellites would be very interesting

[Makoto]

Apollo 15-17 achevied an even lower 'parking' orbit at ~170km before trans lunar injection. These parking orbits are not stable in the long term. It should also be noted that failing/uncontrolled objects like Tiangong-1 made a few orbits at even lower altitudes before reentry.

[StreetIrregular]

Hi Lei, it would be really cool to see a video breaking down the elements of a modern Spaceport. Thanks!

[AnonymousFreakYT]

Minor correction - New Horizons didn't "end its nine year journey successfully" - it's still going! On Jan 1, it will pass Kuiper Belt object (486958) 2014 MU69 (which will get a "real name" after the flyby.) It is even scheduled to pass 1/3 the distance than it did in its pass of Pluto!

[jonathanrazo]

Let's go for a spy satellite video!!

[ejoshcoron]

Love to hear more about the spy satellites Lei