Specs of new downlink

For this scenario a single satellite orbiting in LEO below a megaconstellation placed in LEO is considered.

Latency

According to SpaceX mentioned in the Communication Services project (CSP) poster. less than 100 ms to and from anywhere on earth.

We will do our own calculations at some point.

Throughput

SpaceX advertises a 40-220 MB/s of download speeds for the downlink throughput and a uplink speed of 8-25 MB/s. For now this is what is used for arguments sake, but we should maybe do some calculations ourselves at some point which would include the following.

Bandwidth

This should be the same as the traditional downlink to be able to compare the two. Depending on perspective either the connection should be split in time or in frequency.

SNR

As the signal does not have to travel through a dense atmosphere the SNR of the recieved signal should be higher.

Using the Free-space path loss equation (Friis): $\frac{P_r}{P_t}=D_t{D}_r{\left(\frac{\lambda }{4\pi d}\right)}^2$ where

•  $D_t$ is the directivity of the transmitting antenna
•  $D_r$ is the directivity of the receiving antenna
•  λ is the signal wavelength
•  d is the distance between the antennas

From the SNR and the bandwidth the capacity of the link can be found using the shannon theorem: $C=B\cdot lo{g}_2(1+\frac{S}{N})$ Where B is the bandwidth, S is the average power of the signal and N is the average power of the noise.

Shared connection

As the satellite interacts with the mega constellation as a traditional user, the link would be shared between users in time(or frequency). Therefore the throughput of the satellite depends on the amount of users simultaneous trying to connect using the constellaion. Assuming the connection is shared evenly between the users the throughput would be: $Th=C/U$ Th is the throughput, C is the capacity of the link and U is the number of users.

Price

Something similar to this is the Iridium project (See Stakeholders).

The SpaceX plan for aviation (which is the closest spaceX plan to our idea) is 10 000 $amonthforunlimiteddataand2000$ for 20 GB. Starlink Business | Aviation

Resilience

No dependency on one single groundstation, as these mega constellations has multiple. However if the starlink network is down, there is not much to do since there is no ownership of the groundstations.