Billionaires Anders and Anne Holch Povlsen have asked a senior judge to overturn planning permission for a space port in the Highlands.
The couple own land near the proposed Space Hub Sutherland and have concerns about its impact on protected areas.
Their company Wildland Ltd has raised the legal action against Highland Council’s planning approval.
The project’s backers have said the site, which would be the first of its kind in the UK, will create new jobs.
Planning permission for the facility is being challenged in a judicial review at the Court of Session in Edinburgh.
Lawyers for the Povlsens argued that documents showed Highland Council did not appear to have properly considered the impact that people visiting the site could have on the local environment.
Advocate Malcolm Thomson QC said: “There’s nothing about visitor viewing facilities, car parking, nothing of that nature.
“There are the obvious difficulties about keeping people out of the LEZ (launch exclusion zone) – there’s no physical demarcation of it.”
Public agency Highlands and Islands Enterprise (HIE) has proposed building the facility for launching small satellites on the Moine Peninsula, an area of peatland and crofts on the Highlands’ north coast.
HIE has said the project will create jobs and help boost the Highlands’ and wider Scottish economy.
Highland Council received 457 objections and 118 representations in support of HIE’s planning application.
The impact on the environment, including the Caithness and Sutherland Peatlands Special Protection Area, and risk to human health were among the reasons for objections.
The local authority approved the plans in June and referred its decision to the Scottish government for scrutiny.
In August, Scottish ministers said the plans did not require a decision at national level and should be dealt with by Highland Council.
Danish businessman Mr Povlsen, who is reportedly worth £4.5bn thanks to his Bestseller clothes retail empire, first visited the Highlands on an angling holiday with his parents in the 1980s.
He bought the 42,000-acre Glenfeshie estate in the Cairngorms for £8m in 2006.
Since then, the billionaire, who is the biggest single shareholder in the Asos online retailer, and his wife have bought up huge swathes of the Scottish countryside. They now own about 220,000 acres across 12 estates.
The hearing before Lord Doherty continues.