IEEE Aerospace and Electronic Systems Magazine - July 2020 - 10

Improving Small Satellite Communications in Deep Space
Table 1.

Classiﬁcation of SmallSats for the Purpose of This Study
Type

Transmit power

Antenna
size

Dry mass

Comment

CubeSat

4 W (solid state power amplifier)

0.5 m

About 10 kg

6U CubeSat

MicroSat

30 W (traveling wave tube amplifier)

1.5 m

< 100 kg

Dry mass

spacecraft or, if it lacks a DTE link, the SmallSat must use
a relay satellite to communicate with the ground. Clearly,
the former may function as a relay for the latter. SmallSats
without a DTE link are likely to ride along with a primary
mission's large spacecraft and use the large satellite as
their relay station. However, one can also envision a mix
of SmallSats where some may depend on the others for
relay-this can also include a cluster of SmallSats that
function as a distributed communications system.
Strategies for the observation and the use of radiometric data types for navigation are also considered in this
study. It is noted that SmallSat navigation may be based
on radiometric data collected from a DTE link or from a
cross link (also known as proximity link).
The ground end of a DTE link is assumed to be the DSN.
Therefore, the SmallSat communications architecture must
work within the context of the DSN and take advantage of
initiatives introduced by the DSN to improve network efficiency for SmallSat loading. Thus, the findings of the study
leverage recent loading studies commissioned by the DSN.
There is a large difference between the capabilities
associated with a 100-kg spacecraft and a 6U CubeSat.
For example, the former can carry a much more powerful
amplifier and much bigger antenna than the latter. For this
reason, for convenience, this study focuses on the two
ends of the platform range. The upper range is called
MicroSat and the lower end is called CubeSat. Noting currently available technologies, Table 1 associates the concept of CubeSat and MicroSat with today's available
amplifier power and antenna size (X- and Ka-bands).

SIGNAL BANDS OF INTEREST
The main focus of this article is on the X- and Ka-bands
of the frequency spectrum for Earth/space communications. These bands are popular with planetary missions
due to the availability of ample spectrum allocation for
deep space science; in particular, Ka-band allocation
provides 0.5 GHz of bandwidth both for transmitting
and for receiving, allowing high-rate communications.
Another advantage of these bands with respect to lower
bands is the higher antenna gain associated with them.
This article also discusses optical wavelengths for communications and navigation. Table 2 shows the radio
frequencies allocated to scientific research in the Xand Ka-bands by regulatory bodies for deep space and
near-Earth applications. It should be noted that for relay
(proximity) links, UHF has been the frequency of
choice in the past partly due to the lower cost associated with UHF equipment, however, as we will see in
Part II of this series, the use of higher bands may be
advantageous for certain scenarios.

PUBLICATION SERIES STRUCTURE
We discuss SmallSat DTE links as well as SmallSat communications equipment in this article, Part I. In Part II,
we focus on proximity/relay links, navigation topics, and
the use of SmallSats for radio science observations.
We present the ground network in Part III.

Table 2.

Allocated Frequency Bands (MHz) for Space Research
Band designation

Bands for spacecraft greater than 2
million km from Earth

Bands for spacecraft less than 2
million km from Earth (the Moon
falls in this category)

Uplink

Downlink

Uplink

Downlink

X-band

7145-7190

8400-8450

7190-7235

8450-8500

K-band (a.k.a. Ka2-band)

-

-

22550-23150

25500-27000

Ka-band

34200-34700

31800-32300

-

-

10

IEEE A&E SYSTEMS MAGAZINE

JULY 2020
IEEE Aerospace and Electronic Systems Magazine - July 2020

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