# What orbits are Starlink satellites now deployed into? How low to do they go on their first perigee?

In my answer to Delta-V of Starlink Satellites I ballpark spherical-cow envelope-back estimated 190 m/s with 2 kg of krypton based on raising only from a 445 km circular orbit to a 550 km circular orbit.

raising 445 to 550 km        58 m/s
keeping it there             20 m/s
bringing it down            112 m/s

Total                       190 m/s


I've just watched SpaceX video for January 20, 2021 Starlink Mission and tabulated the altitude (presumably relative to 6378 km) displayed on the screen. Downlink to ground stations is spotty and sometimes the displayed numbers remain fixed for extended periods (don't update) then jump, so I've only included data that seems "live" i.e. is updating regularly when I record the data.

What emerged surprised me!

Callout for SECO-1 at 08:55 was only at 167 km, and at this point altitude was increasing at it's maximum rate until deployment! For such a low eccentricity orbit we can expect altitude to vary roughly sinusoidally with time with a period of about 90 minutes, and to my eye it looks like if nothing is done these satellites will hit the atmosphere in an hour or so.

But this doesn't really look like a sine wave with a period of 90 minutes. Yes the orbit has an inclination of 53 degrees, and considering $$J_2$$ maybe these numbers need to be adjusted for Earth's equatorial bulge, so consider all of this as simply evidence of prior research rather than assertion or premise.

Question: What orbits are Starlink satellites now deployed into? How low to do they go on their first perigee? Do they start raising themselves promptly? Would they "hit the atmosphere" or at least loose a substantial amount of energy on their first perigee if they didn't?

T+ (minutes)  altitude (km)
10             170
15             185
20             201
25             216
30          loss of telemetry
35          loss of telemetry
40             253
45             260
50           loss of telemetry
55           loss of telemetry
60           loss of telemetry
64             286


Starlink January20, 2021 2nd stage altitude after SECO-1 and before deploy

import numpy as np
import matplotlib.pyplot as plt

info = ((10, 170), (15, 185), (20, 201), (25, 216), (40, 253),
(45, 260), (64, 286))

minutes, altitude = np.array(list(zip(*info))).astype(float)

plt.plot(minutes, altitude)
plt.plot(minutes, altitude, 'ok')
plt.xlabel('time since launch (min)')
plt.ylabel('altitude (above 6378 km?)')
plt.show()

"""
T+ (minutes)  altitude (km)
10             170
15             185
20             201
25             216
30          loss of telemetry
35          loss of telemetry
40             253
45             260
50           loss of telemetry
55           loss of telemetry
60           loss of telemetry
64             286
"""

• Did you account for the second stage second burn (@ ~T+44mins in the video you linked)? Jun 2 '21 at 12:16
• @BrendanLuke15 Was there one? All I have to go on is the video and I didn't notice any mention of it. Do you have more info? When was it? There are large gaps in telemetry and I didn't listen to the audio during some stretches.
– uhoh
Jun 2 '21 at 12:19
• Yes there was one, the webcast says it only took one second so I don't blame you for missing it! I will add an answer with more details about the deployment orbit Jun 2 '21 at 12:26
• Great! I noticed that the simulation in flightlcub.io for Starlink v1.0 L16 doesn't mention one either. Thanks!
– uhoh
Jun 2 '21 at 12:28

Jonathan McDowell's Space Report (planet4589.org) website has a page for Starlink statistics. It shows that most Starlinks (check out Starlink L26, rideshare!) deploy from a ~270 km orbit.

I found some TLEs (Space-Track.org) of Falcon 9 second stages & debris from some of the latest Starlink launches that support this (earliest Starlink TLEs that I found show them already at ~290 km and circular):

Starlink L25 second stage debris (May 4th, 19:01 UTC launch):

1 48413U 21038BN  21132.52488535  .00253791  39528-4  39172-3 0  9996
2 48413  53.0519   5.2321 0014496 204.7636 155.2701 16.03554980  1249
Translated:
274 km x 255 km @ May 13, 2021 12:35 UTC


Starlink L27 second stage debris (May 9th, 06:42 UTC launch):

1 48488U 21040BN  21136.63586469  .00218404  32376-4  32510-3 0  9997
2 48488  53.0499 186.9839 0012307 224.9858 135.0177 16.04251274  1185
Translated:
271 km x 254 km @ May 17, 2021 15:15 UTC


Starlink L28 second stage debris (May 26th, 18:59 UTC launch):

1 48701U 21044BR  21152.58405575  .00232318  35463-4  32696-3 0  9994
2 48701  53.0508  36.4200 0016145 183.9666 176.1241 16.05031044   932
Translated:
271 km x 250 km @ June 2, 2021 14:01 UTC


The TLEs are all about a week post launch but since the objects are identified as Falcon 9 debris, they have not changed their orbit since launch and thus give us a good indication of Starlink's initial deployment orbit (add a few kilometers or so to account for a weeks worth of orbital decay).

The second stage performed a second burn in the mission in question at T+45:49 that added 131 km/h (36.4 m/s) of velocity (from webcast telemetry) to circularize the orbit and avoid hitting the discernible atmosphere. I tried doing some crude orbit determination with the limited altitude and velocity data from the webcast. However, it is unclear what the reference frame for the velocity data is, so do not put too much faith in these numbers (notice the growing eccentricity, semi-major axis remains constant though):

Raw Data:

210 km x -653 km coast orbit, 276 km x -615 km final orbit


With initial Earth rotation speed added (221 m/s @ latitude of 28.5°):

220 km x 13 km coast orbit, 279 km x 67 km final orbit


not too shabby

The above linked Starlink statistics page also shows that the satellites appear to start raising their orbits about a day or two after launch, seen in the characteristic decay in orbital height for the first few track points.

• Ah, I see what you did I think; because the TLE's don't show up until about a week after launch, you chose one of these i.stack.imgur.com/6ZgvM.png which most likely never used its own propulsion and exhibits natural orbital decay, and from the TLE got a ~1 week old orbit i.stack.imgur.com/25VXo.png (I used pastebin.com/WD9r30HR) to conclude that it was likely deployed just a little bit higher than this, and therefore would not have hit the atmosphere after deployment?
– uhoh
Jun 2 '21 at 23:52
• I think your observation that there was a second burn of the second stage at around T+00:46:08 is also important to include in the answer as well, as it explains why they don't hit the atmosphere and burn up on their first periapsis which is something I've asked about.
– uhoh
Jun 2 '21 at 23:56
• Great answer, great work; I think if you add a some more of these details I can just accept and call it conclusive. Thanks!
– uhoh
Jun 2 '21 at 23:57