IEEE Aerospace and Electronic Systems Magazine - July 2020 - 34

Improving Small Satellite Communications and Tracking in Deep Space

Figure 6.
MarCO UHF loop antenna mounted on spacecraft (antenna shown deployed).

horizon coverage for MSL relay link support to the Odyssey and MRO orbiters.7
Proximity links typically utilize broad-beam, low-gain
antennas with unique coverage requirements. Existing
antenna designs can be adapted for some applications;
however, since antenna performance can be influenced by
the vehicle mounting environment, new antenna designs
are often needed. For example, most of the antennas illustrated in Figure 4 were new designs developed to meet the
unique MSL mission requirements, but they were subsequently "built to print" for M2020 because the mounting
environment was not changed significantly. The RUHF
antenna has also been adapted for use on the Mars Atmosphere and Volatile Evolution (MAVEN) orbiter [23],
[24] and the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (INSIGHT) lander
[25], and is suitable for many large and medium size landers and orbiters; however, it is too large for SmallSats. For
instance, the MarCO UHF link required a right-hand circularly polarized (RHCP) antenna with gain greater than
2.5 dBi over an azimuth plane coverage area Æ30 from
boresight, a stowed volume of 20 cm Â 20 cm Â 1.6 cm
and mass less than 400 gm. To meet this, a unique new
RHCP deployable square loop antenna was developed
(see Figure 6).
Since UHF has been the primary telecom band for low
earth orbit (LEO) CubeSats, numerous deployable dipoletype antennas have been developed and are commercially
available. Deployable UHF helix antennas have also been
developed for specific applications [26], [27]. Nevertheless,
7

Both Odyssey and MRO are existing Mars communications relay
orbiters.

there is a need to develop CubeSat low-gain proximity
antennas, especially in the UHF band. Currently available
CubeSat antennas were developed for low cost, risk tolerant
LEO missions and have not been qualified for NASA deep
space communications requirements. Moreover, it is important to have a significant range of design options available to
meet the wide variety of requirements and accommodation
issues that can arise in a CubeSat or SmallSat mission. Due
to the fast pace of CubeSat development, it is often not practical to develop a new flight antenna as part of the mission.
Consequently, it would be beneficial for NASA to identify
the range of likely antenna requirements and fund developments in those areas.
As noted earlier, proximity links may also use higher
gain, directional antennas to achieve higher data rates. One
example of this is the deep impact mission [28], which
used an 18 element S-band patch array to achieve 18.5 dBi
gain as required for the data link that provided video of the
comet impactor collision. Since high-gain antennas have a
narrow beamwidth, in most cases a beam pointing mechanism such as a gimbal is required. For instance, a higher
data rate Mars orbiter UHF link to landed assets, such as
MSL or M2020, could be achieved with a 3 Â 3 element
patch array with a $27 beamwidth that provides about 15
dBi gain. However, this would require a mechanical gimbal
to accurately point the 1.5 m Â 1.5 m UHF antenna toward
a rover. Accommodating such a large antenna is difficult
and clearly illustrates the advantage of higher frequencies,
such as X-band, when high data rates are required. Note
that for the same gain, an X-band antenna is about 100
times smaller than its UHF counterpart (surface area).
Active array beam pointing, discussed in Part I, may also
be attractive for this purpose.

IEEE A&E SYSTEMS MAGAZINE

JULY 2020

IEEE Aerospace and Electronic Systems Magazine - July 2020

Table of Contents for the Digital Edition of IEEE Aerospace and Electronic Systems Magazine - July 2020