At least three budding astronauts have dropped out of a private sector-led effort to send a Singaporean into space.
They decided to quit mainly after being asked to pay for the training - something they were not told prior to signing up for the programme.
The former candidates, who spoke to The Sunday Times on condition of anonymity, also expressed concern about the lack of mission details from the venture's leaders, IN.Genius, a local technology firm.
For example, no formal agreement has been made between the firm and the candidates outlining details of matters such as training and costs. Nor has it revealed its space or engineering partners.
The three former candidates said they were shocked when they were told a few months ago that they had to pay for training in skills such as deep-sea diving.
These grouses have surfaced with just over a year to go before National Day next year, when IN.Genius aims to launch from Singapore one pilot in a helium stratospheric balloon craft into near-space, more than 20km above sea level.
Most of the original 26 pilots shortlisted in February were Singapore Airlines pilots. Four were students, one of whom is the 15-year-old daughter of IN.Genius director Lim Seng.
When asked, Mr Lim would say only that "more than 20" of them remain in the running.
To launch its craft from Singapore, the mission needs air space clearance from the Civil Aviation Authority of Singapore (CAAS).
The Sunday Times, however, understands that since exploratory discussions in 2012, IN.Genius - which deals primarily with energy solutions - has not been in touch with the CAAS regarding this.
When pressed about partners, Mr Lim said non-disclosure pacts prevent him from identifying them, saying only that one partner in Europe is designing the balloon and another in Russia is designing the craft's life support system.
IN.Genius itself is leading the overall system engineering, capsule design and avionics, he said.
He revealed for the first time that the mission will cost $5 million to $10 million, is funded by unnamed technopreneurs, and he is consulting "certain space agencies".
The space venture is backed by the Science Centre Board and the Singapore Space and Technology Association, but has not received any government support. Its seven-member advisory panel includes former chief defence scientist Lui Pao Chuen and former Nasa engineer Timothy Kauffman.
Mr Lim said his methods are "maverick" but he intends to fulfil the mission, with or without government funding.
"It is not because we are hiding something but rather there is confidentiality we have to respect," said Mr Lim, who led Singapore's Defence Technology Office in Europe from 1999 to 2004.
He confirmed that candidates were asked to pay for training.
E-mail records showed they were quoted a fee of about $1,200 each to join an eight-day parafoil course in Vietnam next month. Said one former candidate: "It's unfair if we have to pay because if someone isn't able to fund it, he won't be chosen."
Space industry experts here The Sunday Times spoke to had mixed reactions to the latest development.
One who requested not to be named said: "If I'm a candidate, I will tell him, 'Either you show me what's your timeline, what's your spacecraft, who is responsible for what, to make me feel more comfortable, or I'll back out'." But another expert who has worked with Mr Lim said that although his methods are uncommon, he will succeed.
Professor Lui believed the project "will succeed", but added that candidates should also be realistic.