Antenna

Antennae allow communication with Kerbal Space Center, when deployed. With version 0.22 the antennae allow the return of scientific data from space, without the need to recover the craft on Kerbin. Version 1.2 added the requirement of antennae to control unmanned vehicles outside of a specified radius of Kerbin. In prior versions, mods like RemoteTech or Antenna Range add functionality to them.

In versions prior to 0.22, antennae couldn't be retracted and had no function in the base game. A bug could retract them when craft was accessed from the Tracking Station, at the cost of breaking the ability to redeploy them.

Packets

When an antenna transmits data to the Research and Development facility, it consumes an amount of electric charge for each packet of data. The transmission is suspended if there is insufficient electric charge available, and automatically resumes once sufficient stored power is accumulated. The direction and distance as well as the visibility of the facility, that there are no planets or moons in between, don't affect the transmission in any way.

Properties

Each antenna has three transmission properties: packet size (Mits/packet), duration (s/packet), and required energy (⚡/packet). The packet sizes are 1 Mit for the RA-2 Relay Antenna, 3 Mits for the HG-55 Direct Antenna, and 2 Mits for all other stock antennae. Transmissions group the data in a whole number of packets, so the last packet may not be fully utilized. A transmission's total time and required energy can be determined from these properties. For example, consider a materials study (25 Mits) transmitted through a Communotron 16 Antenna (2 Mits/packet, 0.6 s/packet, 12 ⚡/packet). The transmission would be 13 packets and consume 156 ⚡ in 7.8 seconds.

Transmission

When the transmit button is pressed while reviewing experiment results, an antenna will automatically deploy to perform a transmission and then retract after completion. If the antenna's own right-click menu command is used to initiate the transmission, it will attempt to immediately transmit all data stored in all science modules on the craft. Aborting any transmission of scientific data will destroy any remaining data that was to be sent.^[clarify] No warning will be given about this.

When the Transmit button is used and multiple antennae are available, the game chooses the best one based on the cost and time per Mit.

Available antennae

Every probe or command module has an embedded 5k direct antenna. Although they have packet specifications in their cfg file they are unable to transmit science. The only exception is the MPO probe which has an embedded 2G relay antenna with the same specifications than the RA-2 antenna.

Image	Part	Radial size	Cost ()	Mass (t)	Max. Temp. (K)	Tolerance (m/s)	Tolerance (g)	Electricity (⚡/Mit)	Electricity (⚡/s)	Net transmission speed (Mits/s)	Relay capable	CommNet Tier
	Communotron 16	Tiny	300	0.005	2 000	7	50	6	20.0	3.33	No	1
	Communotron 16-S	Radial mounted	300	0.015	2 000	7	50	6	20.0	3.33	No	1
	Communotron DTS-M1	Radial mounted	900	0.05	2 000	8	50	6	34.3	5.71	No	3
	Communotron HG-55	Radial mounted	1200	0.075	2 000	7	50	6.67	133.3	20.0	No	4
	Communotron 88-88	Tiny	1 500	0.1	2 000	7	50	10	200.0	20.0	No	5
	HG-5 High Gain Antenna	Tiny	600	0.07	2 000	8	50	9	51.4	5.71	Yes	2
	RA-2 Relay Antenna	Tiny	1 800	0.15	2 000	8	50	24	68.6	2.86	Yes	3
	RA-15 Relay Antenna	Tiny	2 400	0.3	2 000	8	50	12	68.6	5.71	Yes	4
	RA-100 Relay Antenna	Small	3 000	0.65	2 000	8	50	6	68.6	11.43	Yes	5

Which antenna to use?

A size comparison of the antennas available as of v1.2

For most purposes, it depends how far away you are to Kerbin. Stronger antenna are required to transmit science and control probes the further you are away from the KSC. A list of Antennas and their range can be found in CommNet. Prior to Version 1.2, antenna choice was commonly a matter of aesthetics, choosing based on what fits on the craft in question, and looks good. The impatient may prefer to use the faster antenna (but should ensure that they can generate electricity fast enough, or have a sufficiently large battery supply to keep it running), but even the slowest antenna transmits the largest science experiment data in a tolerable time.

There is no "best" or "better" here, for most purposes. The fast Communotron 88-88 uses almost twice the electricity for the same amount of data, so should possibly be avoided on craft that have a less than generous electricity supply. In a very specific case when only batteries are used the Comms DTS-M1 is better than the Communotron 16, because both use the same amount of electric charge per Mit. On the other hand the Comms DTS-M1 is heavier although the masses are so low that they are probably not important.