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What is this balloon for in this clean room and what is the proper name for the "stand" that is holding the satellite? shows the image below, and a comment below @OrganicMarble's answer there asks:

Is ISRO the only agency to use balloons, or others too use them?

which leads to the more general Question: Is this the only time that a helium balloons was used to support deployed spacecraft appendages during testing on the ground in Earth gravity?

They didn't use a balloon to test the Ingenuity helicopter because they had to test it in a near vacuum, so they used a cable attached to an active system which pulled up with a constant fraction of the flyer's weight. For very heavy things they support them underneath with wheels that roll along the floor.

But a strong, leak-free helium balloon is a pretty nice solution for small loads that need a reliable and fairly steady force upwards.

ISRO helium balloon holding something up

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    $\begingroup$ What kind of answer are you looking for in "how often"? "A lot"? "Not much?" % of payloads ever flown? $\endgroup$ Commented Apr 15, 2021 at 1:03
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    $\begingroup$ @OrganicMarble ya I see what you mean; I've adjusted the wording to make this easier to answer, how does it look now? Goal here is to find out how unusual or common this is, because I don't think I've ever seen this before today. $\endgroup$
    – uhoh
    Commented Apr 15, 2021 at 5:21
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    $\begingroup$ For Chandrayaaan-2 rover mobility tests such balloon was used as well. science.sciencemag.org/content/sci/359/6375/503/F2.large.jpg Source:science.sciencemag.org/content/359/6375/503 $\endgroup$
    – Ohsin
    Commented Apr 29, 2021 at 23:41
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    $\begingroup$ @Ohsin Oh that's wonderful, and wow what a large balloon! Please feel free to write that up as an answer post; future readers may not go through all the comments, comments don't show up in search results the same way posts do, and comments should be considered temporary with the possibility of future deletion. Thanks! $\endgroup$
    – uhoh
    Commented Apr 30, 2021 at 0:04

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For mobility tests of ISRO's Pragyan rover that was part of Chandrayaan-2 lunar orbiter/lander campaign they used a large Helium balloon to counteract 5/6 of Earth's gravity. These tests were conducted in balloon research lab that was modified into a Lunar Terrain Test Facility (LTTF) at ISRO Satellite Integration and Testing Establishment (ISITE) in Bangalore. Later for Chandrayaan-3 campaign these balloons were used again.

"Use of TIFR Balloon Facility and Products in Chandrayaan-3 Mission" (PDF)

Image sources:

For testing CFRP boom deployment on a solar-sail demonstrator spacecraft, Institute of Structural Mechanics of DLR came up with this unique 'gravity compensation' system involving Helium balloons attached with adjustable weights to counteract increasing weight of booms as they were deployed.

enter image description here

The DLR performed a deployment of a light-weight solar sail structure in 1999. The structure consists of four CFRP (Carbon Fiber Reinforced Plastic) booms, each 14 m long, and a rectangular sail with 4 µm to 12 µm thick segments. The beams were highly endangered to collapse under their own weight. They were therefore suspended by helium filled balloons. The mass of the continuously deploying beam increases permanently and thus the suspension forces of the balloons need to be adjusted. This was achieved by remotely controlled pumps draining water from small tanks below the balloons. At mid-deployment four new balloons were attached to support the beams.

"Development and Test of Deployable Ultra-Lightweight CFRP-Booms for a Solar Sail"

"Gravity Compensation of Deployable Solar Arrays for Small Spacecraft"

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Another example is Inflatesail whose inflatable boom deployment testing is shown here.

enter image description here

The buzzword for this support of appendages during ground testing is "g-negation". It's (at least nowadays) more commonly done using air tables supporting from below, wires from controlled structures above, etc. Examples:

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