Early renders of the Orion spacecraft show a deployed high-gain antenna dish like on the Apollo CSM. The Orion that actually materialised has no such thing. What does it use instead?
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The Orion module (capsule + service module) has six antennae, four on the capsule and two on the service module. You can't see them because they're inside either the heat shield on the Orion module or inside the faring that protects the service module.
They are flat (or nearly so), but that does not mean they are omnidirectional antennae. They are instead phased array antennae. There are key advantages to a phased array antenna compared to a dish antenna:
- No moving parts. A highly directional dish antenna either needs the spacecraft to change its orientation (which can interfere with operations and costs propellant) or it needs a drive motor (which can fail) so the dish points at the Earth. A phased array antenna does not need to do either but can still be highly direction. The aiming is instead done with electronics that differentially delay the signal from / to different parts of the antenna.
- Quick response. This is a side benefit from having no moving parts. Reorienting a spacecraft or a drive motor that controls an antenna is a slow process. Changing the phasing is extremely quick.
- Hidden from view (and more importantly, protected from debris and sunlight). A big dish antenna has to stick out from the spacecraft. The Orion antennae are flat and are protected.
answered Dec 1, 2022 at 22:33
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$\begingroup$ Could planetary spacecraft use phase array antennas instead of large dishes? $\endgroup$– AndykinsCommented Dec 2, 2022 at 9:59
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2$\begingroup$ @Andykins Yes. That was exactly what the MESSENGER probe to Mercury used. $\endgroup$ Commented Dec 2, 2022 at 11:15